diff --git a/modules/backend/classes/Controller.php b/modules/backend/classes/Controller.php
index 77d2aaecd..a95a068f6 100644
--- a/modules/backend/classes/Controller.php
+++ b/modules/backend/classes/Controller.php
@@ -339,7 +339,7 @@ class Controller extends Extendable
                 $responseContents = [];
                 $responseContents['#layout-flash-messages'] = $this->makeLayoutPartial('flash_messages');
                 $responseContents['X_OCTOBER_ERROR_FIELDS'] = $ex->getFields();
-                return Response::make()->setContent($responseContents);
+                return Response::make($responseContents, 406);
             }
             catch (Exception $ex) {
                 Log::error($ex);
diff --git a/modules/system/assets/js/framework.js b/modules/system/assets/js/framework.js
index 292975be5..ed4332e21 100644
--- a/modules/system/assets/js/framework.js
+++ b/modules/system/assets/js/framework.js
@@ -140,7 +140,7 @@ if (window.jQuery === undefined)
                 var _event = jQuery.Event('ajaxErrorMessage')
                 $(window).trigger(_event, [message])
                 if (_event.isDefaultPrevented()) return
-                alert(message)
+                if (message) alert(message)
             },
 
             /*
diff --git a/modules/system/classes/PluginManager.php b/modules/system/classes/PluginManager.php
index 501a6c7ae..70569b66a 100644
--- a/modules/system/classes/PluginManager.php
+++ b/modules/system/classes/PluginManager.php
@@ -256,6 +256,9 @@ class PluginManager
         if (!isset($this->plugins[$identifier]))
             $identifier = $this->normalizeIdentifier($identifier);
 
+        if (!isset($this->plugins[$identifier]))
+            return null;
+
         return $this->plugins[$identifier];
     }