diff --git a/ghost/admin/app/app.js b/ghost/admin/app/app.js
index 0818b24930..942d76a33a 100755
--- a/ghost/admin/app/app.js
+++ b/ghost/admin/app/app.js
@@ -2,6 +2,7 @@ import Ember from 'ember';
 import Application from 'ember-application';
 import Resolver from './resolver';
 import loadInitializers from 'ember-load-initializers';
+import 'ghost-admin/utils/route';
 import 'ghost-admin/utils/link-component';
 import 'ghost-admin/utils/text-field';
 import config from './config/environment';
diff --git a/ghost/admin/app/components/gh-file-uploader.js b/ghost/admin/app/components/gh-file-uploader.js
index 45bd3f3306..0df6cf3227 100644
--- a/ghost/admin/app/components/gh-file-uploader.js
+++ b/ghost/admin/app/components/gh-file-uploader.js
@@ -7,6 +7,7 @@ import run from 'ember-runloop';
 
 import { invoke, invokeAction } from 'ember-invoke-action';
 import {
+    isVersionMismatchError,
     isRequestEntityTooLargeError,
     isUnsupportedMediaTypeError
 } from 'ghost-admin/services/ajax';
@@ -28,6 +29,7 @@ export default Component.extend({
     uploadPercentage: 0,
 
     ajax: injectService(),
+    notifications: injectService(),
 
     formData: computed('file', function () {
         let paramName = this.get('paramName');
@@ -128,6 +130,10 @@ export default Component.extend({
     _uploadFailed(error) {
         let message;
 
+        if (isVersionMismatchError(error)) {
+            this.get('notifications').showAPIError(error);
+        }
+
         if (isUnsupportedMediaTypeError(error)) {
             message = 'The file type you uploaded is not supported.';
         } else if (isRequestEntityTooLargeError(error)) {
diff --git a/ghost/admin/app/components/gh-image-uploader.js b/ghost/admin/app/components/gh-image-uploader.js
index 51c322d867..86b3b27161 100644
--- a/ghost/admin/app/components/gh-image-uploader.js
+++ b/ghost/admin/app/components/gh-image-uploader.js
@@ -5,10 +5,12 @@ import {htmlSafe} from 'ember-string';
 import {isBlank} from 'ember-utils';
 import run from 'ember-runloop';
 
+import {invokeAction} from 'ember-invoke-action';
 import ghostPaths from 'ghost-admin/utils/ghost-paths';
 import {
     isRequestEntityTooLargeError,
-    isUnsupportedMediaTypeError
+    isUnsupportedMediaTypeError,
+    isVersionMismatchError
 } from 'ghost-admin/services/ajax';
 
 export default Component.extend({
@@ -29,6 +31,7 @@ export default Component.extend({
 
     ajax: injectService(),
     config: injectService(),
+    notifications: injectService(),
 
     // TODO: this wouldn't be necessary if the server could accept direct
     // file uploads
@@ -114,13 +117,11 @@ export default Component.extend({
         }
     },
 
-    uploadStarted() {
-        if (typeof this.attrs.uploadStarted === 'function') {
-            this.attrs.uploadStarted();
-        }
+    _uploadStarted() {
+        invokeAction(this, 'uploadStarted');
     },
 
-    uploadProgress(event) {
+    _uploadProgress(event) {
         if (event.lengthComputable) {
             run(() => {
                 let percentage = Math.round((event.loaded / event.total) * 100);
@@ -129,21 +130,24 @@ export default Component.extend({
         }
     },
 
-    uploadFinished() {
-        if (typeof this.attrs.uploadFinished === 'function') {
-            this.attrs.uploadFinished();
-        }
+    _uploadFinished() {
+        invokeAction(this, 'uploadFinished');
     },
 
-    uploadSuccess(response) {
+    _uploadSuccess(response) {
         this.set('url', response);
         this.send('saveUrl');
         this.send('reset');
+        invokeAction(this, 'uploadSuccess', response);
     },
 
-    uploadFailed(error) {
+    _uploadFailed(error) {
         let message;
 
+        if (isVersionMismatchError(error)) {
+            this.get('notifications').showAPIError(error);
+        }
+
         if (isUnsupportedMediaTypeError(error)) {
             message = 'The image type you uploaded is not supported. Please use .PNG, .JPG, .GIF, .SVG.';
         } else if (isRequestEntityTooLargeError(error)) {
@@ -155,6 +159,7 @@ export default Component.extend({
         }
 
         this.set('failureMessage', message);
+        invokeAction(this, 'uploadFailed', error);
     },
 
     generateRequest() {
@@ -162,7 +167,7 @@ export default Component.extend({
         let formData = this.get('formData');
         let url = `${ghostPaths().apiRoot}/uploads/`;
 
-        this.uploadStarted();
+        this._uploadStarted();
 
         ajax.post(url, {
             data: formData,
@@ -173,18 +178,18 @@ export default Component.extend({
                 let xhr = new window.XMLHttpRequest();
 
                 xhr.upload.addEventListener('progress', (event) => {
-                    this.uploadProgress(event);
+                    this._uploadProgress(event);
                 }, false);
 
                 return xhr;
             }
         }).then((response) => {
             let url = JSON.parse(response);
-            this.uploadSuccess(url);
+            this._uploadSuccess(url);
         }).catch((error) => {
-            this.uploadFailed(error);
+            this._uploadFailed(error);
         }).finally(() => {
-            this.uploadFinished();
+            this._uploadFinished();
         });
     },
 
@@ -198,10 +203,7 @@ export default Component.extend({
 
         onInput(url) {
             this.set('url', url);
-
-            if (typeof this.attrs.onInput === 'function') {
-                this.attrs.onInput(url);
-            }
+            invokeAction(this, 'onInput', url);
         },
 
         reset() {
@@ -212,16 +214,14 @@ export default Component.extend({
         switchForm(formType) {
             this.set('formType', formType);
 
-            if (typeof this.attrs.formChanged === 'function') {
-                run.scheduleOnce('afterRender', this, function () {
-                    this.attrs.formChanged(formType);
-                });
-            }
+            run.scheduleOnce('afterRender', this, function () {
+                invokeAction(this, 'formChanged', formType);
+            });
         },
 
         saveUrl() {
             let url = this.get('url');
-            this.attrs.update(url);
+            invokeAction(this, 'update', url);
         }
     }
 });
diff --git a/ghost/admin/app/components/gh-search-input.js b/ghost/admin/app/components/gh-search-input.js
index 7a4164d6c1..a634294f67 100644
--- a/ghost/admin/app/components/gh-search-input.js
+++ b/ghost/admin/app/components/gh-search-input.js
@@ -39,6 +39,7 @@ export default Component.extend({
     _store: injectService('store'),
     _routing: injectService('-routing'),
     ajax: injectService(),
+    notifications: injectService(),
 
     refreshContent() {
         let promises = [];
@@ -91,7 +92,6 @@ export default Component.extend({
         let content = this.get('content');
 
         return this.get('ajax').request(postsUrl, {data: postsQuery}).then((posts) => {
-
             content.pushObjects(posts.posts.map((post) => {
                 return {
                     id: `post.${post.id}`,
@@ -99,6 +99,8 @@ export default Component.extend({
                     category: post.page ? 'Pages' : 'Posts'
                 };
             }));
+        }).catch((error) => {
+            this.get('notifications').showAPIError(error, {key: 'search.loadPosts.error'});
         });
     },
 
@@ -116,6 +118,8 @@ export default Component.extend({
                     category: 'Users'
                 };
             }));
+        }).catch((error) => {
+            this.get('notifications').showAPIError(error, {key: 'search.loadUsers.error'});
         });
     },
 
@@ -133,6 +137,8 @@ export default Component.extend({
                     category: 'Tags'
                 };
             }));
+        }).catch((error) => {
+            this.get('notifications').showAPIError(error, {key: 'search.loadTags.error'});
         });
     },
 
diff --git a/ghost/admin/app/components/modals/invite-new-user.js b/ghost/admin/app/components/modals/invite-new-user.js
index a32f413f7b..61c6dc8e5f 100644
--- a/ghost/admin/app/components/modals/invite-new-user.js
+++ b/ghost/admin/app/components/modals/invite-new-user.js
@@ -1,6 +1,6 @@
 import RSVP from 'rsvp';
 import injectService from 'ember-service/inject';
-import {A as emberA} from 'ember-array/utils';
+import {A as emberA, isEmberArray} from 'ember-array/utils';
 import run from 'ember-runloop';
 import ModalComponent from 'ghost-admin/components/modals/base';
 import ValidationEngine from 'ghost-admin/mixins/validation-engine';
@@ -113,7 +113,11 @@ export default ModalComponent.extend(ValidationEngine, {
                     }
                 }).catch((errors) => {
                     newUser.deleteRecord();
-                    notifications.showErrors(errors, {key: 'invite.send'});
+                    if (isEmberArray(errors)) {
+                        notifications.showErrors(errors, {key: 'invite.send'});
+                    } else {
+                        notifications.showAPIError(errors, {key: 'invite.send'});
+                    }
                 }).finally(() => {
                     this.send('closeModal');
                 });
diff --git a/ghost/admin/app/components/modals/new-subscriber.js b/ghost/admin/app/components/modals/new-subscriber.js
index f4870c2ad5..a371c0968c 100644
--- a/ghost/admin/app/components/modals/new-subscriber.js
+++ b/ghost/admin/app/components/modals/new-subscriber.js
@@ -16,12 +16,26 @@ export default ModalComponent.extend({
 
             confirmAction().then(() => {
                 this.send('closeModal');
-            }).catch((errors) => {
-                let [error] = errors;
-                if (error && error.match(/email/i)) {
-                    this.get('model.errors').add('email', error);
-                    this.get('model.hasValidated').pushObject('email');
+            }).catch((error) => {
+                // TODO: server-side validation errors should be serialized
+                // properly so that errors are added to the model's errors
+                // property
+                if (error && error.isAdapterError) {
+                    let [firstError] = error.errors;
+                    let {message, errorType} = firstError;
+
+                    if (errorType === 'ValidationError') {
+                        if (message && message.match(/email/i)) {
+                            this.get('model.errors').add('email', message);
+                            this.get('model.hasValidated').pushObject('email');
+                            return;
+                        }
+                    }
                 }
+
+                // this is a route action so it should bubble up to the global
+                // error handler
+                throw error;
             }).finally(() => {
                 if (!this.get('isDestroying') && !this.get('isDestroyed')) {
                     this.set('submitting', false);
diff --git a/ghost/admin/app/components/modals/re-authenticate.js b/ghost/admin/app/components/modals/re-authenticate.js
index 2124278177..51d91ddb24 100644
--- a/ghost/admin/app/components/modals/re-authenticate.js
+++ b/ghost/admin/app/components/modals/re-authenticate.js
@@ -4,6 +4,7 @@ import injectService from 'ember-service/inject';
 import {htmlSafe} from 'ember-string';
 import ModalComponent from 'ghost-admin/components/modals/base';
 import ValidationEngine from 'ghost-admin/mixins/validation-engine';
+import {isVersionMismatchError} from 'ghost-admin/services/ajax';
 
 export default ModalComponent.extend(ValidationEngine, {
     validationType: 'signin',
@@ -49,6 +50,9 @@ export default ModalComponent.extend(ValidationEngine, {
                 }).catch((error) => {
                     if (error && error.errors) {
                         error.errors.forEach((err) => {
+                            if (isVersionMismatchError(err)) {
+                                return this.get('notifications').showAPIError(error);
+                            }
                             err.message = htmlSafe(err.message);
                         });
 
diff --git a/ghost/admin/app/controllers/post-settings-menu.js b/ghost/admin/app/controllers/post-settings-menu.js
index 08eb33f9d1..8ebad097ca 100644
--- a/ghost/admin/app/controllers/post-settings-menu.js
+++ b/ghost/admin/app/controllers/post-settings-menu.js
@@ -16,6 +16,7 @@ import {parseDateString} from 'ghost-admin/utils/date-formatting';
 import SettingsMenuMixin from 'ghost-admin/mixins/settings-menu-controller';
 import boundOneWay from 'ghost-admin/utils/bound-one-way';
 import isNumber from 'ghost-admin/utils/isNumber';
+import {isVersionMismatchError} from 'ghost-admin/services/ajax';
 
 const {ArrayProxy, Handlebars, PromiseProxyMixin} = Ember;
 
@@ -74,10 +75,13 @@ export default Controller.extend(SettingsMenuMixin, {
                 if (!isBlank(slug)) {
                     this.set(destination, slug);
                 }
-            }).catch(() => {
+            }).catch((error) => {
                 // Nothing to do (would be nice to log this somewhere though),
                 // but a rejected promise needs to be handled here so that a resolved
                 // promise is returned.
+                if (isVersionMismatchError(error)) {
+                    this.get('notifications').showAPIError(error);
+                }
             });
         });
 
@@ -181,6 +185,9 @@ export default Controller.extend(SettingsMenuMixin, {
     }),
 
     showErrors(errors) {
+        if (isVersionMismatchError(errors)) {
+            return this.get('notifications').showAPIError(errors);
+        }
         errors = isEmberArray(errors) ? errors : [errors];
         this.get('notifications').showErrors(errors);
     },
diff --git a/ghost/admin/app/controllers/settings/apps/slack.js b/ghost/admin/app/controllers/settings/apps/slack.js
index fe8d678189..1ee3e18ea1 100644
--- a/ghost/admin/app/controllers/settings/apps/slack.js
+++ b/ghost/admin/app/controllers/settings/apps/slack.js
@@ -33,6 +33,7 @@ export default Controller.extend({
                     notifications.showAlert('Check your slack channel test message.', {type: 'info', key: 'slack-test.send.success'});
                 }).catch((error) => {
                     notifications.showAPIError(error, {key: 'slack-test:send'});
+                    throw error;
                 });
             }).catch(() => {
                 // noop - error already handled in .save
@@ -60,7 +61,9 @@ export default Controller.extend({
                 this.set('isSaving', true);
 
                 return settings.save().catch((err) => {
-                    this.get('notifications').showErrors(err);
+                    if (err && err.isAdapterError) {
+                        this.get('notifications').showAPIError(err);
+                    }
                     throw err;
                 }).finally(() => {
                     this.set('isSaving', false);
diff --git a/ghost/admin/app/controllers/settings/navigation.js b/ghost/admin/app/controllers/settings/navigation.js
index 24064abf4b..d1df5d3337 100644
--- a/ghost/admin/app/controllers/settings/navigation.js
+++ b/ghost/admin/app/controllers/settings/navigation.js
@@ -38,7 +38,7 @@ export default Controller.extend(SettingsSaveMixin, {
 
         return RSVP.all(validationPromises).then(() => {
             return this.get('model').save().catch((err) => {
-                notifications.showErrors(err);
+                notifications.showAPIError(err);
             });
         }).catch(() => {
             // TODO: noop - needed to satisfy spinner button
diff --git a/ghost/admin/app/controllers/signin.js b/ghost/admin/app/controllers/signin.js
index cd9d3b73ca..b2932d95b4 100644
--- a/ghost/admin/app/controllers/signin.js
+++ b/ghost/admin/app/controllers/signin.js
@@ -4,6 +4,10 @@ import injectService from 'ember-service/inject';
 import injectController from 'ember-controller/inject';
 import {isEmberArray} from 'ember-array/utils';
 
+import {
+    VersionMismatchError,
+    isVersionMismatchError
+} from 'ghost-admin/services/ajax';
 import ValidationEngine from 'ghost-admin/mixins/validation-engine';
 
 export default Controller.extend(ValidationEngine, {
@@ -31,6 +35,14 @@ export default Controller.extend(ValidationEngine, {
                 this.toggleProperty('loggingIn');
 
                 if (error && error.errors) {
+                    // we don't get back an ember-data/ember-ajax error object
+                    // back so we need to pass in a null status in order to
+                    // test against the payload
+                    if (isVersionMismatchError(null, error)) {
+                        let versionMismatchError = new VersionMismatchError(error);
+                        return this.get('notifications').showAPIError(versionMismatchError);
+                    }
+
                     error.errors.forEach((err) => {
                         err.message = err.message.htmlSafe();
                     });
@@ -62,12 +74,8 @@ export default Controller.extend(ValidationEngine, {
             this.validate({property: 'signin'}).then(() => {
                 this.toggleProperty('loggingIn');
                 this.send('authenticate');
-            }).catch((error) => {
-                if (error) {
-                    this.get('notifications').showAPIError(error, {key: 'signin.authenticate'});
-                } else {
-                    this.set('flowErrors', 'Please fill out the form to sign in.');
-                }
+            }).catch(() => {
+                this.set('flowErrors', 'Please fill out the form to sign in.');
             });
         },
 
@@ -89,11 +97,15 @@ export default Controller.extend(ValidationEngine, {
                 }).then(() => {
                     this.toggleProperty('submitting');
                     notifications.showAlert('Please check your email for instructions.', {type: 'info', key: 'forgot-password.send.success'});
-                }).catch((resp) => {
+                }).catch((error) => {
                     this.toggleProperty('submitting');
 
-                    if (resp && resp.errors && isEmberArray(resp.errors)) {
-                        let [{message}] = resp.errors;
+                    if (isVersionMismatchError(error)) {
+                        return notifications.showAPIError(error);
+                    }
+
+                    if (error && error.errors && isEmberArray(error.errors)) {
+                        let [{message}] = error.errors;
 
                         this.set('flowErrors', message);
 
@@ -101,7 +113,7 @@ export default Controller.extend(ValidationEngine, {
                             this.get('model.errors').add('identification', '');
                         }
                     } else {
-                        notifications.showAPIError(resp, {defaultErrorText: 'There was a problem with the reset, please try again.', key: 'forgot-password.send'});
+                        notifications.showAPIError(error, {defaultErrorText: 'There was a problem with the reset, please try again.', key: 'forgot-password.send'});
                     }
                 });
             }).catch(() => {
diff --git a/ghost/admin/app/controllers/signup.js b/ghost/admin/app/controllers/signup.js
index c275690dde..ad59d4392e 100644
--- a/ghost/admin/app/controllers/signup.js
+++ b/ghost/admin/app/controllers/signup.js
@@ -4,6 +4,7 @@ import injectService from 'ember-service/inject';
 import {isEmberArray} from 'ember-array/utils';
 
 import ValidationEngine from 'ghost-admin/mixins/validation-engine';
+import {isVersionMismatchError} from 'ghost-admin/services/ajax';
 
 const {Promise} = RSVP;
 
@@ -74,13 +75,16 @@ export default Controller.extend(ValidationEngine, {
                     }).catch((resp) => {
                         notifications.showAPIError(resp, {key: 'signup.complete'});
                     });
-                }).catch((resp) => {
+                }).catch((error) => {
                     this.toggleProperty('submitting');
 
-                    if (resp && resp.errors && isEmberArray(resp.errors)) {
-                        this.set('flowErrors', resp.errors[0].message);
+                    if (error && error.errors && isEmberArray(error.errors)) {
+                        if (isVersionMismatchError(error)) {
+                            notifications.showAPIError(error);
+                        }
+                        this.set('flowErrors', error.errors[0].message);
                     } else {
-                        notifications.showAPIError(resp, {key: 'signup.complete'});
+                        notifications.showAPIError(error, {key: 'signup.complete'});
                     }
                 });
             }).catch(() => {
diff --git a/ghost/admin/app/controllers/team/user.js b/ghost/admin/app/controllers/team/user.js
index 4054406680..aa343c95dd 100644
--- a/ghost/admin/app/controllers/team/user.js
+++ b/ghost/admin/app/controllers/team/user.js
@@ -141,8 +141,10 @@ export default Controller.extend({
 
                 return model;
             }).catch((errors) => {
-                if (errors) {
+                if (isEmberArray(errors)) {
                     this.get('notifications').showErrors(errors, {key: 'user.update'});
+                } else {
+                    this.get('notifications').showAPIError(errors);
                 }
 
                 this.toggleProperty('submitting');
diff --git a/ghost/admin/app/initializers/upgrade-status.js b/ghost/admin/app/initializers/upgrade-status.js
new file mode 100644
index 0000000000..1baa0ca92b
--- /dev/null
+++ b/ghost/admin/app/initializers/upgrade-status.js
@@ -0,0 +1,8 @@
+export function initialize(application) {
+    application.inject('route', 'upgradeStatus', 'service:upgrade-status');
+}
+
+export default {
+    name: 'upgrade-status',
+    initialize
+};
diff --git a/ghost/admin/app/mirage/config.js b/ghost/admin/app/mirage/config.js
index 27045d871c..3b504a0cce 100644
--- a/ghost/admin/app/mirage/config.js
+++ b/ghost/admin/app/mirage/config.js
@@ -8,6 +8,16 @@ const {
     String: {dasherize}
 } = Ember;
 
+/* jshint unused:false */
+function versionMismatchResponse() {
+    return new Mirage.Response(400, {}, {
+        errors: [{
+            errorType: 'VersionMismatchError'
+        }]
+    });
+}
+/* jshint unused:true */
+
 function paginatedResponse(modelName, allModels, request) {
     let page = +request.queryParams.page || 1;
     let limit = request.queryParams.limit || 15;
@@ -122,7 +132,7 @@ export default function () {
     this.timing = 400;      // delay for each request, automatically set to 0 during testing
 
     // Mock endpoints here to override real API requests during development
-    mockSubscribers(this);
+    // this.put('/posts/:id/', versionMismatchResponse);
 
     // keep this line, it allows all other API requests to hit the real server
     this.passthrough();
@@ -211,13 +221,20 @@ export function testConfig() {
         return response;
     });
 
-    this.get('/posts/:id', function (db, request) {
+    this.get('/posts/:id/', function (db, request) {
         let {id} = request.params;
         let post = db.posts.find(id);
 
-        return {
-            posts: [post]
-        };
+        if (!post) {
+            return new Mirage.Response(404, {}, {
+                errors: [{
+                    errorType: 'NotFoundError',
+                    message: 'Post not found.'
+                }]
+            });
+        } else {
+            return {posts: [post]};
+        }
     });
 
     this.put('/posts/:id/', function (db, request) {
diff --git a/ghost/admin/app/mixins/404-handler.js b/ghost/admin/app/mixins/404-handler.js
deleted file mode 100644
index a0977a1c80..0000000000
--- a/ghost/admin/app/mixins/404-handler.js
+++ /dev/null
@@ -1,23 +0,0 @@
-import Mixin from 'ember-metal/mixin';
-
-export default Mixin.create({
-    actions: {
-        error(error, transition) {
-            if (error.errors && error.errors[0].errorType === 'NotFoundError') {
-                transition.abort();
-
-                let routeInfo = transition.handlerInfos[transition.handlerInfos.length - 1];
-                let router = this.get('router');
-                let params = [];
-
-                for (let key of Object.keys(routeInfo.params)) {
-                    params.push(routeInfo.params[key]);
-                }
-
-                return this.transitionTo('error404', router.generate(routeInfo.name, ...params).replace('/ghost/', '').replace(/^\//g, ''));
-            }
-
-            return this._super(...arguments);
-        }
-    }
-});
diff --git a/ghost/admin/app/mixins/editor-base-controller.js b/ghost/admin/app/mixins/editor-base-controller.js
index e169663f30..cce49fc644 100644
--- a/ghost/admin/app/mixins/editor-base-controller.js
+++ b/ghost/admin/app/mixins/editor-base-controller.js
@@ -403,10 +403,19 @@ export default Mixin.create({
                     }
                     return model;
                 });
-            }).catch((errors) => {
+            }).catch((error) => {
+                // re-throw if we have a general server error
+                // TODO: use isValidationError(error) once we have
+                // ember-ajax/ember-data integration
+                if (error && error.errors && error.errors[0].errorType !== 'ValidationError') {
+                    this.toggleProperty('submitting');
+                    this.send('error', error);
+                    return;
+                }
+
                 if (!options.silent) {
-                    errors = errors || this.get('model.errors.messages');
-                    this.showErrorAlert(prevStatus, this.get('model.status'), errors);
+                    error = error || this.get('model.errors.messages');
+                    this.showErrorAlert(prevStatus, this.get('model.status'), error);
                 }
 
                 this.set('model.status', prevStatus);
diff --git a/ghost/admin/app/mixins/editor-base-route.js b/ghost/admin/app/mixins/editor-base-route.js
index c514f158d9..94865e6536 100644
--- a/ghost/admin/app/mixins/editor-base-route.js
+++ b/ghost/admin/app/mixins/editor-base-route.js
@@ -49,6 +49,10 @@ export default Mixin.create(styleBody, ShortcutsRoute, {
             let deletedWithoutChanges,
                 fromNewToEdit;
 
+            if (this.get('upgradeStatus.isRequired')) {
+                return this._super(...arguments);
+            }
+
             // if a save is in-flight we don't know whether or not it's safe to leave
             // so we abort the transition and retry after the save has completed.
             if (state.isSaving) {
diff --git a/ghost/admin/app/mixins/pagination.js b/ghost/admin/app/mixins/pagination.js
index df412efc61..f801d03b68 100644
--- a/ghost/admin/app/mixins/pagination.js
+++ b/ghost/admin/app/mixins/pagination.js
@@ -4,8 +4,6 @@ import computed from 'ember-computed';
 import RSVP from 'rsvp';
 import injectService from 'ember-service/inject';
 
-import getRequestErrorMessage from 'ghost-admin/utils/ajax';
-
 let defaultPaginationSettings = {
     page: 1,
     limit: 15
@@ -40,25 +38,11 @@ export default Mixin.create({
         this.set('paginationMeta', {});
     },
 
-    /**
-     * Takes an ajax response, concatenates any error messages, then generates an error notification.
-     * @param {jqXHR} response The jQuery ajax reponse object.
-     * @return
-     */
-    reportLoadError(response) {
-        let message = 'A problem was encountered while loading more records';
-
-        if (response) {
-            // Get message from response
-            message += `: ${getRequestErrorMessage(response, true)}`;
-        } else {
-            message += '.';
-        }
-
-        this.get('notifications').showAlert(message, {type: 'error', key: 'pagination.load.failed'});
+    reportLoadError(error) {
+        this.get('notifications').showAPIError(error, {key: 'pagination.load.failed'});
     },
 
-    loadFirstPage() {
+    loadFirstPage(transition) {
         let paginationSettings = this.get('paginationSettings');
         let modelName = this.get('paginationModel');
 
@@ -69,8 +53,14 @@ export default Mixin.create({
         return this.get('store').query(modelName, paginationSettings).then((results) => {
             this.set('paginationMeta', results.meta);
             return results;
-        }).catch((response) => {
-            this.reportLoadError(response);
+        }).catch((error) => {
+            // if we have a transition we're executing in a route hook so we
+            // want to throw in order to trigger the global error handler
+            if (transition) {
+                throw error;
+            } else {
+                this.reportLoadError(error);
+            }
         }).finally(() => {
             this.set('isLoading', false);
         });
@@ -99,8 +89,8 @@ export default Mixin.create({
                 return store.query(modelName, paginationSettings).then((results) => {
                     this.set('paginationMeta', results.meta);
                     return results;
-                }).catch((response) => {
-                    this.reportLoadError(response);
+                }).catch((error) => {
+                    this.reportLoadError(error);
                 }).finally(() => {
                     this.set('isLoading', false);
                 });
diff --git a/ghost/admin/app/mixins/validation-engine.js b/ghost/admin/app/mixins/validation-engine.js
index 4f4b01405b..8dee7f9c85 100644
--- a/ghost/admin/app/mixins/validation-engine.js
+++ b/ghost/admin/app/mixins/validation-engine.js
@@ -3,7 +3,6 @@ import RSVP from 'rsvp';
 import {A as emberA, isEmberArray} from 'ember-array/utils';
 import DS from 'ember-data';
 import Model from 'ember-data/model';
-import getRequestErrorMessage from 'ghost-admin/utils/ajax';
 
 import InviteUserValidator from 'ghost-admin/validators/invite-user';
 import NavItemValidator from 'ghost-admin/validators/nav-item';
@@ -146,8 +145,7 @@ export default Mixin.create({
         }).catch((result) => {
             // server save failed or validator type doesn't exist
             if (result && !isEmberArray(result)) {
-                // return the array of errors from the server
-                result = getRequestErrorMessage(result);
+                throw result;
             }
 
             return RSVP.reject(result);
diff --git a/ghost/admin/app/routes/application.js b/ghost/admin/app/routes/application.js
index f261d1197e..f433143137 100644
--- a/ghost/admin/app/routes/application.js
+++ b/ghost/admin/app/routes/application.js
@@ -2,6 +2,7 @@ import Route from 'ember-route';
 import {htmlSafe} from 'ember-string';
 import injectService from 'ember-service/inject';
 import run from 'ember-runloop';
+import {isEmberArray} from 'ember-array/utils';
 
 import AuthConfiguration from 'ember-simple-auth/configuration';
 import ApplicationRouteMixin from 'ember-simple-auth/mixins/application-route-mixin';
@@ -146,6 +147,46 @@ export default Route.extend(ApplicationRouteMixin, ShortcutsRoute, {
         },
 
         // noop default for unhandled save (used from shortcuts)
-        save: K
+        save: K,
+
+        error(error, transition) {
+            if (error && isEmberArray(error.errors)) {
+                switch (error.errors[0].errorType) {
+
+                    case 'NotFoundError':
+                        if (transition) {
+                            transition.abort();
+                        }
+
+                        let routeInfo = transition.handlerInfos[transition.handlerInfos.length - 1];
+                        let router = this.get('router');
+                        let params = [];
+
+                        for (let key of Object.keys(routeInfo.params)) {
+                            params.push(routeInfo.params[key]);
+                        }
+
+                        return this.transitionTo('error404', router.generate(routeInfo.name, ...params).replace('/ghost/', '').replace(/^\//g, ''));
+
+                    case 'VersionMismatchError':
+                        if (transition) {
+                            transition.abort();
+                        }
+
+                        this.get('upgradeStatus').requireUpgrade();
+                        return false;
+
+                    default:
+                        this.get('notifications').showAPIError(error);
+                        // don't show the 500 page if we weren't navigating
+                        if (!transition) {
+                            return false;
+                        }
+                }
+            }
+
+            // fallback to 500 error page
+            return true;
+        }
     }
 });
diff --git a/ghost/admin/app/routes/editor/edit.js b/ghost/admin/app/routes/editor/edit.js
index fb89ab41c0..a3a1108ea6 100644
--- a/ghost/admin/app/routes/editor/edit.js
+++ b/ghost/admin/app/routes/editor/edit.js
@@ -1,11 +1,10 @@
 /* jscs:disable requireCamelCaseOrUpperCaseIdentifiers */
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
 import base from 'ghost-admin/mixins/editor-base-route';
-import NotFoundHandler from 'ghost-admin/mixins/404-handler';
 import isNumber from 'ghost-admin/utils/isNumber';
 import isFinite from 'ghost-admin/utils/isFinite';
 
-export default AuthenticatedRoute.extend(base, NotFoundHandler, {
+export default AuthenticatedRoute.extend(base, {
     titleToken: 'Editor',
 
     beforeModel(transition) {
diff --git a/ghost/admin/app/routes/posts/post.js b/ghost/admin/app/routes/posts/post.js
index b39a643d3d..33646c8883 100644
--- a/ghost/admin/app/routes/posts/post.js
+++ b/ghost/admin/app/routes/posts/post.js
@@ -1,10 +1,9 @@
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
 import ShortcutsRoute from 'ghost-admin/mixins/shortcuts-route';
-import NotFoundHandler from 'ghost-admin/mixins/404-handler';
 import isNumber from 'ghost-admin/utils/isNumber';
 import isFinite from 'ghost-admin/utils/isFinite';
 
-export default AuthenticatedRoute.extend(ShortcutsRoute, NotFoundHandler, {
+export default AuthenticatedRoute.extend(ShortcutsRoute, {
     model(params) {
         let post,
             postId,
diff --git a/ghost/admin/app/routes/settings/tags.js b/ghost/admin/app/routes/settings/tags.js
index 6c7944ef65..9c241aab4c 100644
--- a/ghost/admin/app/routes/settings/tags.js
+++ b/ghost/admin/app/routes/settings/tags.js
@@ -29,8 +29,8 @@ export default AuthenticatedRoute.extend(CurrentUserSettings, PaginationMixin, S
             .then(this.transitionAuthor());
     },
 
-    model() {
-        return this.loadFirstPage().then(() => {
+    model(params, transition) {
+        return this.loadFirstPage(transition).then(() => {
             return this.store.filter('tag', (tag) => {
                 return !tag.get('isNew');
             });
diff --git a/ghost/admin/app/routes/settings/tags/tag.js b/ghost/admin/app/routes/settings/tags/tag.js
index 628be8d08a..08097f83f7 100644
--- a/ghost/admin/app/routes/settings/tags/tag.js
+++ b/ghost/admin/app/routes/settings/tags/tag.js
@@ -1,8 +1,7 @@
 /* jscs:disable requireCamelCaseOrUpperCaseIdentifiers */
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
-import NotFoundHandler from 'ghost-admin/mixins/404-handler';
 
-export default AuthenticatedRoute.extend(NotFoundHandler, {
+export default AuthenticatedRoute.extend({
 
     model(params) {
         return this.store.queryRecord('tag', {slug: params.tag_slug});
diff --git a/ghost/admin/app/routes/setup/one.js b/ghost/admin/app/routes/setup/one.js
index fe19ab92f6..8f6a1a5d30 100644
--- a/ghost/admin/app/routes/setup/one.js
+++ b/ghost/admin/app/routes/setup/one.js
@@ -15,6 +15,7 @@ let DownloadCountPoller = EmberObject.extend({
     runId: null,
 
     ajax: AjaxService.create(),
+    notifications: injectService(),
 
     init() {
         this._super(...arguments);
@@ -44,8 +45,9 @@ let DownloadCountPoller = EmberObject.extend({
             }
 
             this.set('count', count);
-        }).catch(() => {
+        }).catch((error) => {
             this.set('count', '');
+            this.get('notifications').showAPIError(error);
         });
     }
 });
diff --git a/ghost/admin/app/routes/team/user.js b/ghost/admin/app/routes/team/user.js
index 12fddeadeb..5e68d4b3e8 100644
--- a/ghost/admin/app/routes/team/user.js
+++ b/ghost/admin/app/routes/team/user.js
@@ -2,9 +2,8 @@
 import AuthenticatedRoute from 'ghost-admin/routes/authenticated';
 import CurrentUserSettings from 'ghost-admin/mixins/current-user-settings';
 import styleBody from 'ghost-admin/mixins/style-body';
-import NotFoundHandler from 'ghost-admin/mixins/404-handler';
 
-export default AuthenticatedRoute.extend(styleBody, CurrentUserSettings, NotFoundHandler, {
+export default AuthenticatedRoute.extend(styleBody, CurrentUserSettings, {
     titleToken: 'Team - User',
 
     classNames: ['team-view-user'],
diff --git a/ghost/admin/app/services/ajax.js b/ghost/admin/app/services/ajax.js
index 6b392e224f..ccc93f819f 100644
--- a/ghost/admin/app/services/ajax.js
+++ b/ghost/admin/app/services/ajax.js
@@ -1,3 +1,4 @@
+import get from 'ember-metal/get';
 import computed from 'ember-computed';
 import injectService from 'ember-service/inject';
 import {isEmberArray} from 'ember-array/utils';
@@ -5,34 +6,58 @@ import AjaxService from 'ember-ajax/services/ajax';
 import {AjaxError, isAjaxError} from 'ember-ajax/errors';
 import config from 'ghost-admin/config/environment';
 
+/* Version mismatch error */
+
+export function VersionMismatchError(errors) {
+    AjaxError.call(this, errors, 'API server is running a newer version of Ghost, please upgrade.');
+}
+
+VersionMismatchError.prototype = Object.create(AjaxError.prototype);
+
+export function isVersionMismatchError(errorOrStatus, payload) {
+    if (isAjaxError(errorOrStatus)) {
+        return errorOrStatus instanceof VersionMismatchError;
+    } else if (errorOrStatus && get(errorOrStatus, 'isAdapterError')) {
+        return get(errorOrStatus, 'errors.firstObject.errorType') === 'VersionMismatchError';
+    } else {
+        return get(payload || {}, 'errors.firstObject.errorType') === 'VersionMismatchError';
+    }
+}
+
+/* Request entity too large error */
+
 export function RequestEntityTooLargeError(errors) {
     AjaxError.call(this, errors, 'Request was rejected because it\'s larger than the maximum file size the server allows');
 }
 
 RequestEntityTooLargeError.prototype = Object.create(AjaxError.prototype);
 
-export function isRequestEntityTooLargeError(error) {
-    if (isAjaxError(error)) {
-        return error instanceof RequestEntityTooLargeError;
+export function isRequestEntityTooLargeError(errorOrStatus) {
+    if (isAjaxError(errorOrStatus)) {
+        return errorOrStatus instanceof RequestEntityTooLargeError;
     } else {
-        return error === 413;
+        return errorOrStatus === 413;
     }
 }
 
+/* Unsupported media type error */
+
 export function UnsupportedMediaTypeError(errors) {
     AjaxError.call(this, errors, 'Request was rejected because it contains an unknown or unsupported file type.');
 }
 
 UnsupportedMediaTypeError.prototype = Object.create(AjaxError.prototype);
 
-export function isUnsupportedMediaTypeError(error) {
-    if (isAjaxError(error)) {
-        return error instanceof UnsupportedMediaTypeError;
+export function isUnsupportedMediaTypeError(errorOrStatus) {
+    if (isAjaxError(errorOrStatus)) {
+        return errorOrStatus instanceof UnsupportedMediaTypeError;
     } else {
-        return error === 415;
+        return errorOrStatus === 415;
     }
 }
 
+/* end: custom error types */
+
 export default AjaxService.extend({
     session: injectService(),
 
@@ -52,7 +77,9 @@ export default AjaxService.extend({
     }).volatile(),
 
     handleResponse(status, headers, payload) {
-        if (this.isRequestEntityTooLargeError(status, headers, payload)) {
+        if (this.isVersionMismatchError(status, headers, payload)) {
+            return new VersionMismatchError(payload.errors);
+        } else if (this.isRequestEntityTooLargeError(status, headers, payload)) {
             return new RequestEntityTooLargeError(payload.errors);
         } else if (this.isUnsupportedMediaTypeError(status, headers, payload)) {
             return new UnsupportedMediaTypeError(payload.errors);
@@ -79,6 +106,10 @@ export default AjaxService.extend({
         return this._super(status, headers, payload);
     },
 
+    isVersionMismatchError(status, headers, payload) {
+        return isVersionMismatchError(status, payload);
+    },
+
     isRequestEntityTooLargeError(status/*, headers, payload */) {
         return isRequestEntityTooLargeError(status);
     },
diff --git a/ghost/admin/app/services/feature.js b/ghost/admin/app/services/feature.js
index 5546b4271d..7e1f0eda1d 100644
--- a/ghost/admin/app/services/feature.js
+++ b/ghost/admin/app/services/feature.js
@@ -65,17 +65,17 @@ export default Service.extend({
             this.notifyPropertyChange('labs');
             return this.get(`labs.${key}`);
 
-        }).catch((errors) => {
+        }).catch((error) => {
             settings.rollbackAttributes();
             this.notifyPropertyChange('labs');
 
             // we'll always have an errors object unless we hit a
             // validation error
-            if (!errors) {
+            if (!error) {
                 throw new EmberError(`Validation of the feature service settings model failed when updating labs.`);
             }
 
-            this.get('notifications').showErrors(errors);
+            this.get('notifications').showAPIError(error);
 
             return this.get(`labs.${key}`);
         });
diff --git a/ghost/admin/app/services/notifications.js b/ghost/admin/app/services/notifications.js
index 10b071e9db..399137b875 100644
--- a/ghost/admin/app/services/notifications.js
+++ b/ghost/admin/app/services/notifications.js
@@ -3,7 +3,8 @@ import {filter} from 'ember-computed';
 import {A as emberA, isEmberArray} from 'ember-array/utils';
 import get from 'ember-metal/get';
 import set from 'ember-metal/set';
-import {isAjaxError} from 'ember-ajax/errors';
+import injectService from 'ember-service/inject';
+import {isVersionMismatchError} from 'ghost-admin/services/ajax';
 
 // Notification keys take the form of "noun.verb.message", eg:
 //
@@ -18,6 +19,8 @@ export default Service.extend({
     delayedNotifications: emberA(),
     content: emberA(),
 
+    upgradeStatus: injectService(),
+
     alerts: filter('content', function (notification) {
         let status = get(notification, 'status');
         return status === 'alert';
@@ -99,6 +102,22 @@ export default Service.extend({
     },
 
     showAPIError(resp, options) {
+        // handle "global" errors
+        if (isVersionMismatchError(resp)) {
+            return this.get('upgradeStatus').requireUpgrade();
+        }
+
+        // loop over Ember Data / ember-ajax errors object
+        if (resp && isEmberArray(resp.errors)) {
+            return resp.errors.forEach((error) => {
+                this._showAPIError(error, options);
+            });
+        }
+
+        this._showAPIError(resp, options);
+    },
+
+    _showAPIError(resp, options) {
         options = options || {};
         options.type = options.type || 'error';
         // TODO: getting keys from the server would be useful here (necessary for i18n)
@@ -110,12 +129,10 @@ export default Service.extend({
 
         options.defaultErrorText = options.defaultErrorText || 'There was a problem on the server, please try again.';
 
-        if (isAjaxError(resp)) {
-            resp = resp.errors;
-        }
-
         if (resp && isEmberArray(resp) && resp.length) { // Array of errors
             this.showErrors(resp, options);
+        } else if (resp && resp.message) {
+            this.showAlert(resp.message, options);
         } else if (resp && resp.detail) { // ember-ajax provided error message
             this.showAlert(resp.detail, options);
         } else { // text error or no error
diff --git a/ghost/admin/app/services/upgrade-status.js b/ghost/admin/app/services/upgrade-status.js
new file mode 100644
index 0000000000..76a7822c6c
--- /dev/null
+++ b/ghost/admin/app/services/upgrade-status.js
@@ -0,0 +1,16 @@
+import Service from 'ember-service';
+import injectService from 'ember-service/inject';
+
+export default Service.extend({
+    isRequired: false,
+
+    notifications: injectService(),
+
+    requireUpgrade() {
+        this.set('isRequired', true);
+        this.get('notifications').showAlert(
+            'Ghost has been upgraded, please copy any unsaved data and refresh the page to continue.',
+            {type: 'error', key: 'api-error.upgrade-required'}
+        );
+    }
+});
diff --git a/ghost/admin/app/styles/components/notifications.css b/ghost/admin/app/styles/components/notifications.css
index 1131e51106..932a65f11d 100644
--- a/ghost/admin/app/styles/components/notifications.css
+++ b/ghost/admin/app/styles/components/notifications.css
@@ -130,7 +130,7 @@
 
 /* Base alert style */
 .gh-alert {
-    z-index: 1000;
+    z-index: 9999;
     flex-grow: 1;
     display: flex;
     justify-content: space-between;
diff --git a/ghost/admin/app/templates/components/modals/import-subscribers.hbs b/ghost/admin/app/templates/components/modals/import-subscribers.hbs
index e04b2aa9c7..ae0085095d 100644
--- a/ghost/admin/app/templates/components/modals/import-subscribers.hbs
+++ b/ghost/admin/app/templates/components/modals/import-subscribers.hbs
@@ -34,9 +34,9 @@
             url=uploadUrl
             paramName="subscribersfile"
             labelText="Select or drag-and-drop a CSV file."
-            uploadStarted=(action 'uploadStarted')
-            uploadFinished=(action 'uploadFinished')
-            uploadSuccess=(action 'uploadSuccess')}}
+            uploadStarted=(action "uploadStarted")
+            uploadFinished=(action "uploadFinished")
+            uploadSuccess=(action "uploadSuccess")}}
     {{/liquid-if}}
 </div>
 
diff --git a/ghost/admin/app/templates/subscribers/import.hbs b/ghost/admin/app/templates/subscribers/import.hbs
index 35ede97005..a8c10927d7 100644
--- a/ghost/admin/app/templates/subscribers/import.hbs
+++ b/ghost/admin/app/templates/subscribers/import.hbs
@@ -1,3 +1,4 @@
 {{gh-fullscreen-modal "import-subscribers"
     confirm=(route-action "reset")
-    close=(route-action "cancel")}}
+    close=(route-action "cancel")
+    modifier="action wide"}}
diff --git a/ghost/admin/app/utils/route.js b/ghost/admin/app/utils/route.js
new file mode 100644
index 0000000000..69369dd12c
--- /dev/null
+++ b/ghost/admin/app/utils/route.js
@@ -0,0 +1,15 @@
+import Route from 'ember-route';
+
+Route.reopen({
+    actions: {
+        willTransition(transition) {
+            if (this.get('upgradeStatus.isRequired')) {
+                transition.abort();
+                this.get('upgradeStatus').requireUpgrade();
+                return false;
+            } else {
+                this._super(...arguments);
+            }
+        }
+    }
+});
diff --git a/ghost/admin/tests/acceptance/editor-test.js b/ghost/admin/tests/acceptance/editor-test.js
index 557d8405a8..0b4aa394e4 100644
--- a/ghost/admin/tests/acceptance/editor-test.js
+++ b/ghost/admin/tests/acceptance/editor-test.js
@@ -24,6 +24,8 @@ describe('Acceptance: Editor', function() {
     });
 
     it('redirects to signin when not authenticated', function () {
+        server.create('post');
+
         invalidateSession(application);
         visit('/editor/1');
 
@@ -35,6 +37,7 @@ describe('Acceptance: Editor', function() {
     it('does not redirect to team page when authenticated as author', function () {
         let role = server.create('role', {name: 'Author'});
         let user = server.create('user', {roles: [role], slug: 'test-user'});
+        server.create('post');
 
         authenticateSession(application);
         visit('/editor/1');
@@ -47,6 +50,7 @@ describe('Acceptance: Editor', function() {
     it('does not redirect to team page when authenticated as editor', function () {
         let role = server.create('role', {name: 'Editor'});
         let user = server.create('user', {roles: [role], slug: 'test-user'});
+        server.create('post');
 
         authenticateSession(application);
         visit('/editor/1');
@@ -56,6 +60,19 @@ describe('Acceptance: Editor', function() {
         });
     });
 
+    it('displays 404 when post does not exist', function () {
+        let role = server.create('role', {name: 'Editor'});
+        let user = server.create('user', {roles: [role], slug: 'test-user'});
+
+        authenticateSession(application);
+        visit('/editor/1');
+
+        andThen(() => {
+            expect(currentPath()).to.equal('error404');
+            expect(currentURL()).to.equal('/editor/1');
+        });
+    });
+
     describe('when logged in', function () {
 
         beforeEach(function () {
diff --git a/ghost/admin/tests/acceptance/settings/slack-test.js b/ghost/admin/tests/acceptance/settings/slack-test.js
index 0f6b986995..c578268cc3 100644
--- a/ghost/admin/tests/acceptance/settings/slack-test.js
+++ b/ghost/admin/tests/acceptance/settings/slack-test.js
@@ -108,6 +108,7 @@ describe('Acceptance: Settings - Apps - Slack', function () {
             click('.gh-alert-blue .gh-alert-close');
             click('#sendTestNotification');
 
+            // we shouldn't try to send the test request if the save fails
             andThen(() => {
                 let [lastRequest] = server.pretender.handledRequests.slice(-1);
                 expect(lastRequest.url).to.not.match(/\/slack\/test/);
diff --git a/ghost/admin/tests/acceptance/version-mismatch-test.js b/ghost/admin/tests/acceptance/version-mismatch-test.js
new file mode 100644
index 0000000000..16f1013097
--- /dev/null
+++ b/ghost/admin/tests/acceptance/version-mismatch-test.js
@@ -0,0 +1,133 @@
+/* jshint expr:true */
+import {
+    describe,
+    it,
+    beforeEach,
+    afterEach
+} from 'mocha';
+import { expect } from 'chai';
+import startApp from '../helpers/start-app';
+import destroyApp from '../helpers/destroy-app';
+import { invalidateSession, authenticateSession } from 'ghost-admin/tests/helpers/ember-simple-auth';
+import Mirage from 'ember-cli-mirage';
+
+let versionMismatchResponse = function () {
+    return new Mirage.Response(400, {}, {
+        errors: [{
+            errorType: 'VersionMismatchError',
+            statusCode: 400
+        }]
+    });
+};
+
+describe('Acceptance: Version Mismatch', function() {
+    let application;
+
+    beforeEach(function() {
+        application = startApp();
+    });
+
+    afterEach(function() {
+        destroyApp(application);
+    });
+
+    describe('logged in', function () {
+        beforeEach(function () {
+            let role = server.create('role', {name: 'Administrator'});
+            let user = server.create('user', {roles: [role]});
+
+            server.loadFixtures();
+
+            return authenticateSession(application);
+        });
+
+        it('displays an alert and disables navigation when saving', function () {
+            server.createList('post', 3);
+
+            // mock the post save endpoint to return version mismatch
+            server.put('/posts/:id', versionMismatchResponse);
+
+            visit('/');
+            click('.posts-list li:nth-of-type(2) a'); // select second post
+            click('.post-edit'); // preview edit button
+            click('.js-publish-button'); // "Save post"
+
+            andThen(() => {
+                // has the refresh to update alert
+                expect(find('.gh-alert').length).to.equal(1);
+                expect(find('.gh-alert').text()).to.match(/refresh/);
+            });
+
+            // try navigating back to the content list
+            click('.gh-nav-main-content');
+
+            andThen(() => {
+                expect(currentPath()).to.equal('editor.edit');
+            });
+        });
+
+        it('displays alert and aborts the transition when navigating', function () {
+            // mock the tags endpoint to return version mismatch
+            server.get('/tags/', versionMismatchResponse);
+
+            visit('/');
+            click('.gh-nav-settings-tags');
+
+            andThen(() => {
+                // navigation is blocked
+                expect(currentPath()).to.equal('posts.index');
+
+                // has the refresh to update alert
+                expect(find('.gh-alert').length).to.equal(1);
+                expect(find('.gh-alert').text()).to.match(/refresh/);
+            });
+        });
+
+        it('displays alert and aborts the transition when an ember-ajax error is thrown whilst navigating', function () {
+            server.get('/configuration/timezones/', versionMismatchResponse);
+
+            visit('/settings/tags');
+            click('.gh-nav-settings-general');
+
+            andThen(() => {
+                // navigation is blocked
+                expect(currentPath()).to.equal('settings.tags.index');
+
+                // has the refresh to update alert
+                expect(find('.gh-alert').length).to.equal(1);
+                expect(find('.gh-alert').text()).to.match(/refresh/);
+            });
+        });
+
+        it('can be triggered when passed in to a component', function () {
+            server.post('/subscribers/csv/', versionMismatchResponse);
+
+            visit('/subscribers');
+            click('.btn:contains("Import CSV")');
+            fileUpload('.fullscreen-modal input[type="file"]');
+
+            andThen(() => {
+                // alert is shown
+                expect(find('.gh-alert').length).to.equal(1);
+                expect(find('.gh-alert').text()).to.match(/refresh/);
+            });
+        });
+    });
+
+    describe('logged out', function () {
+        it('displays alert', function () {
+            server.post('/authentication/token', versionMismatchResponse);
+
+            visit('/signin');
+            fillIn('[name="identification"]', 'test@example.com');
+            fillIn('[name="password"]', 'password');
+            click('.btn-blue');
+
+            andThen(() => {
+                // has the refresh to update alert
+                expect(find('.gh-alert').length).to.equal(1);
+                expect(find('.gh-alert').text()).to.match(/refresh/);
+            });
+        });
+    });
+});
diff --git a/ghost/admin/tests/integration/components/gh-file-uploader-test.js b/ghost/admin/tests/integration/components/gh-file-uploader-test.js
index 738347c229..e17a143b36 100644
--- a/ghost/admin/tests/integration/components/gh-file-uploader-test.js
+++ b/ghost/admin/tests/integration/components/gh-file-uploader-test.js
@@ -11,6 +11,13 @@ import Pretender from 'pretender';
 import wait from 'ember-test-helpers/wait';
 import sinon from 'sinon';
 import {createFile, fileUpload} from '../../helpers/file-upload';
+import Service from 'ember-service';
+
+const notificationsStub = Service.extend({
+    showAPIError(error, options) {
+        // noop - to be stubbed
+    }
+});
 
 const stubSuccessfulUpload = function (server, delay = 0) {
     server.post('/ghost/api/v0.1/uploads/', function () {
@@ -41,6 +48,9 @@ describeComponent(
         beforeEach(function () {
             server = new Pretender();
             this.set('uploadUrl', '/ghost/api/v0.1/uploads/');
+
+            this.register('service:notifications', notificationsStub);
+            this.inject.service('notifications', {as: 'notifications'});
         });
 
         afterEach(function () {
@@ -217,6 +227,35 @@ describeComponent(
             });
         });
 
+        it('triggers notifications.showAPIError for VersionMismatchError', function (done) {
+            let showAPIError = sinon.spy();
+            this.set('notifications.showAPIError', showAPIError);
+
+            stubFailedUpload(server, 400, 'VersionMismatchError');
+
+            this.render(hbs`{{gh-file-uploader url=uploadUrl}}`);
+            fileUpload(this.$('input[type="file"]'));
+
+            wait().then(() => {
+                expect(showAPIError.calledOnce).to.be.true;
+                done();
+            });
+        });
+
+        it('doesn\'t trigger notifications.showAPIError for other errors', function (done) {
+            let showAPIError = sinon.spy();
+            this.set('notifications.showAPIError', showAPIError);
+
+            stubFailedUpload(server, 400, 'UnknownError');
+            this.render(hbs`{{gh-file-uploader url=uploadUrl}}`);
+            fileUpload(this.$('input[type="file"]'));
+
+            wait().then(() => {
+                expect(showAPIError.called).to.be.false;
+                done();
+            });
+        });
+
         it('can be reset after a failed upload', function (done) {
             stubFailedUpload(server, 400, 'UnknownError');
             this.render(hbs`{{gh-file-uploader url=uploadUrl}}`);
diff --git a/ghost/admin/tests/integration/components/gh-image-uploader-test.js b/ghost/admin/tests/integration/components/gh-image-uploader-test.js
index c951956276..90d5a2e220 100644
--- a/ghost/admin/tests/integration/components/gh-image-uploader-test.js
+++ b/ghost/admin/tests/integration/components/gh-image-uploader-test.js
@@ -21,6 +21,12 @@ const configStub = Service.extend({
     fileStorage: true
 });
 
+const notificationsStub = Service.extend({
+    showAPIError(error, options) {
+        // noop - to be stubbed
+    }
+});
+
 const sessionStub = Service.extend({
     isAuthenticated: false,
     authorize(authorizer, block) {
@@ -59,8 +65,10 @@ describeComponent(
         beforeEach(function () {
             this.register('service:config', configStub);
             this.register('service:session', sessionStub);
+            this.register('service:notifications', notificationsStub);
             this.inject.service('config', {as: 'configService'});
             this.inject.service('session', {as: 'sessionService'});
+            this.inject.service('notifications', {as: 'notifications'});
             this.set('update', function () {});
             server = new Pretender();
         });
@@ -298,6 +306,35 @@ describeComponent(
                 });
             });
 
+            it('triggers notifications.showAPIError for VersionMismatchError', function (done) {
+                let showAPIError = sinon.spy();
+                this.set('notifications.showAPIError', showAPIError);
+
+                stubFailedUpload(server, 400, 'VersionMismatchError');
+
+                this.render(hbs`{{gh-image-uploader image=image update=(action update)}}`);
+                fileUpload(this.$('input[type="file"]'));
+
+                wait().then(() => {
+                    expect(showAPIError.calledOnce).to.be.true;
+                    done();
+                });
+            });
+
+            it('doesn\'t trigger notifications.showAPIError for other errors', function (done) {
+                let showAPIError = sinon.spy();
+                this.set('notifications.showAPIError', showAPIError);
+
+                stubFailedUpload(server, 400, 'UnknownError');
+                this.render(hbs`{{gh-image-uploader image=image update=(action update)}}`);
+                fileUpload(this.$('input[type="file"]'));
+
+                wait().then(() => {
+                    expect(showAPIError.called).to.be.false;
+                    done();
+                });
+            });
+
             it('can be reset after a failed upload', function (done) {
                 stubFailedUpload(server, 400, 'UnknownError');
                 this.render(hbs`{{gh-image-uploader image=image update=(action update)}}`);
diff --git a/ghost/admin/tests/integration/components/gh-search-input-test.js b/ghost/admin/tests/integration/components/gh-search-input-test.js
index 82c9139daa..8074f75de6 100644
--- a/ghost/admin/tests/integration/components/gh-search-input-test.js
+++ b/ghost/admin/tests/integration/components/gh-search-input-test.js
@@ -6,7 +6,18 @@ import {
 } from 'ember-mocha';
 import hbs from 'htmlbars-inline-precompile';
 import run from 'ember-runloop';
+import Pretender from 'pretender';
 import wait from 'ember-test-helpers/wait';
+import sinon from 'sinon';
+
+let versionMismatchResponse = function () {
+    return [400, {'Content-Type': 'application/json'}, JSON.stringify({
+        errors: [{
+            errorType: 'VersionMismatchError',
+            statusCode: 400
+        }]
+    })];
+};
 
 describeComponent(
     'gh-search-input',
@@ -15,6 +26,16 @@ describeComponent(
         integration: true
     },
     function () {
+        let server;
+
+        beforeEach(function () {
+            server = new Pretender();
+        });
+
+        afterEach(function () {
+            server.shutdown();
+        });
+
         it('renders', function () {
             // renders the component on the page
             this.render(hbs`{{gh-search-input}}`);
diff --git a/ghost/admin/tests/integration/services/ajax-test.js b/ghost/admin/tests/integration/services/ajax-test.js
index 1c9abdfd03..acd58d2973 100644
--- a/ghost/admin/tests/integration/services/ajax-test.js
+++ b/ghost/admin/tests/integration/services/ajax-test.js
@@ -9,6 +9,7 @@ import {
     isUnauthorizedError
 } from 'ember-ajax/errors';
 import {
+    isVersionMismatchError,
     isRequestEntityTooLargeError,
     isUnsupportedMediaTypeError
 } from 'ghost-admin/services/ajax';
@@ -125,6 +126,30 @@ describeModule(
             });
         });
 
+        it('handles error checking for VersionMismatchError', function (done) {
+            server.get('/test/', function () {
+                return [
+                    400,
+                    {'Content-Type': 'application/json'},
+                    JSON.stringify({
+                        errors: [{
+                            errorType: 'VersionMismatchError',
+                            statusCode: 400
+                        }]
+                    })
+                ];
+            });
+
+            let ajax = this.subject();
+
+            ajax.request('/test/').then(() => {
+                expect(false).to.be.true;
+            }).catch((error) => {
+                expect(isVersionMismatchError(error)).to.be.true;
+                done();
+            });
+        });
+
         it('handles error checking for RequestEntityTooLargeError on 413 errors', function (done) {
             stubAjaxEndpoint(server, {}, 413);
 
diff --git a/ghost/admin/tests/integration/services/feature-test.js b/ghost/admin/tests/integration/services/feature-test.js
index 01265a00eb..1828acd7d6 100644
--- a/ghost/admin/tests/integration/services/feature-test.js
+++ b/ghost/admin/tests/integration/services/feature-test.js
@@ -174,8 +174,16 @@ describeModule(
                 });
 
                 return wait().then(() => {
-                    expect(server.handlers[1].numberOfCalls).to.equal(1);
-                    expect(service.get('notifications.notifications').length).to.equal(1);
+                    expect(
+                        server.handlers[1].numberOfCalls,
+                        'PUT call is made'
+                    ).to.equal(1);
+
+                    expect(
+                        service.get('notifications.alerts').length,
+                        'number of alerts shown'
+                    ).to.equal(1);
+
                     expect(service.get('testFlag')).to.be.false;
                     done();
                 });
diff --git a/ghost/admin/tests/unit/controllers/settings/navigation-test.js b/ghost/admin/tests/unit/controllers/settings/navigation-test.js
index 318784f7a6..418c185e4d 100644
--- a/ghost/admin/tests/unit/controllers/settings/navigation-test.js
+++ b/ghost/admin/tests/unit/controllers/settings/navigation-test.js
@@ -25,7 +25,14 @@ describeModule(
     'Unit: Controller: settings/navigation',
     {
         // Specify the other units that are required for this test.
-        needs: ['service:config', 'service:notifications', 'model:navigation-item', 'service:ajax', 'service:ghostPaths']
+        needs: [
+            'service:config',
+            'service:notifications',
+            'model:navigation-item',
+            'service:ajax',
+            'service:ghostPaths',
+            'service:upgrade-status'
+        ]
     },
     function () {
         it('blogUrl: captures config and ensures trailing slash', function () {
diff --git a/ghost/admin/tests/unit/services/notifications-test.js b/ghost/admin/tests/unit/services/notifications-test.js
index c1fed1f87d..73bad6459e 100644
--- a/ghost/admin/tests/unit/services/notifications-test.js
+++ b/ghost/admin/tests/unit/services/notifications-test.js
@@ -166,34 +166,39 @@ describeModule(
             ]);
         });
 
-        it('#showAPIError adds single json response error', function () {
+        it('#showAPIError handles single json response error', function () {
             let notifications = this.subject();
-            let error = new AjaxError('Single error');
+            let error = new AjaxError([{message: 'Single error'}]);
 
             run(() => {
                 notifications.showAPIError(error);
             });
 
-            let notification = notifications.get('alerts.firstObject');
-            expect(get(notification, 'message')).to.equal('Single error');
-            expect(get(notification, 'status')).to.equal('alert');
-            expect(get(notification, 'type')).to.equal('error');
-            expect(get(notification, 'key')).to.equal('api-error');
+            let alert = notifications.get('alerts.firstObject');
+            expect(get(alert, 'message')).to.equal('Single error');
+            expect(get(alert, 'status')).to.equal('alert');
+            expect(get(alert, 'type')).to.equal('error');
+            expect(get(alert, 'key')).to.equal('api-error');
         });
 
-        // used to display validation errors returned from the server
-        it('#showAPIError adds multiple json response errors', function () {
+        // TODO: update once we have unique api key handling
+        it('#showAPIError handles multiple json response errors', function () {
             let notifications = this.subject();
-            let error = new AjaxError(['First error', 'Second error']);
+            let error = new AjaxError([
+                {message: 'First error'},
+                {message: 'Second error'}
+            ]);
 
             run(() => {
                 notifications.showAPIError(error);
             });
 
-            expect(notifications.get('notifications')).to.deep.equal([
-                {message: 'First error', status: 'notification', type: 'error', key: undefined},
-                {message: 'Second error', status: 'notification', type: 'error', key: undefined}
-            ]);
+            // First error is removed due to duplicate api-key
+            let alert = notifications.get('alerts.firstObject');
+            expect(get(alert, 'message')).to.equal('Second error');
+            expect(get(alert, 'status')).to.equal('alert');
+            expect(get(alert, 'type')).to.equal('error');
+            expect(get(alert, 'key')).to.equal('api-error');
         });
 
         it('#showAPIError displays default error text if response has no error/message', function () {
@@ -238,7 +243,7 @@ describeModule(
 
         it('#showAPIError parses errors from ember-ajax correctly', function () {
             let notifications = this.subject();
-            let error = new InvalidError('Test Error');
+            let error = new InvalidError([{message: 'Test Error'}]);
 
             run(() => {
                 notifications.showAPIError(error);
diff --git a/ghost/admin/tests/unit/services/upgrade-status-test.js b/ghost/admin/tests/unit/services/upgrade-status-test.js
new file mode 100644
index 0000000000..cc7d35c7ba
--- /dev/null
+++ b/ghost/admin/tests/unit/services/upgrade-status-test.js
@@ -0,0 +1,23 @@
+/* jshint expr:true */
+import { expect } from 'chai';
+import {
+    describeModule,
+    it
+} from 'ember-mocha';
+
+describeModule(
+    'service:upgrade-status',
+    'UpgradeStatusService',
+    {
+        // Specify the other units that are required for this test.
+        // needs: ['service:foo']
+        needs: []
+    },
+    function() {
+        // Replace this with your real tests.
+        it('exists', function() {
+            let service = this.subject();
+            expect(service).to.be.ok;
+        });
+    }
+);