diff --git a/js/h5p-content-upgrade.js b/js/h5p-content-upgrade.js
index bbea037..5be3428 100644
--- a/js/h5p-content-upgrade.js
+++ b/js/h5p-content-upgrade.js
@@ -2,18 +2,18 @@ var H5PUpgrades = H5PUpgrades || {};
 
 (function ($) {
   var info, $container, librariesCache = {};
-  
+
   // Initialize
   $(document).ready(function () {
     // Get library info
     info = H5PIntegration.getLibraryInfo();
-    
+
     // Get and reset container
     $container = $('#h5p-admin-container').html('<p>' + info.message + '</p>');
-    
+
     // Make it possible to select version
     var $version = $(getVersionSelect(info.versions)).appendTo($container);
-    
+
     // Add "go" button
     $('<button/>', {
       class: 'h5p-admin-upgrade-button',
@@ -23,11 +23,11 @@ var H5PUpgrades = H5PUpgrades || {};
         new ContentUpgrade($version.val());
       }
     }).appendTo($container);
-  });  
+  });
 
   /**
    * Generate html for version select.
-   *  
+   *
    * @param {Object} versions
    * @returns {String}
    */
@@ -41,18 +41,18 @@ var H5PUpgrades = H5PUpgrades || {};
       return html;
     }
   };
-  
+
   /**
    * Private. Helps process each property on the given object asynchronously in serial order.
-   * 
+   *
    * @param {Object} obj
    * @param {Function} process
    * @param {Function} finished
    */
   var asyncSerial = function (obj, process, finished) {
     var id, isArray = obj instanceof Array;
-    
-    // Keep track of each property that belongs to this object. 
+
+    // Keep track of each property that belongs to this object.
     if (!isArray) {
       var ids = [];
       for (id in obj) {
@@ -61,9 +61,9 @@ var H5PUpgrades = H5PUpgrades || {};
         }
       }
     }
-    
+
     var i = -1; // Keeps track of the current property
-    
+
     /**
      * Private. Process the next property
      */
@@ -71,10 +71,10 @@ var H5PUpgrades = H5PUpgrades || {};
       id = isArray ? i : ids[i];
       process(id, obj[id], check);
     };
-    
+
     /**
      * Private. Check if we're done or have an error.
-     *  
+     *
      * @param {String} err
      */
     var check = function (err) {
@@ -89,13 +89,13 @@ var H5PUpgrades = H5PUpgrades || {};
         }
       }, 0);
     };
-    
+
     check(); // Start
   };
 
-  /** 
+  /**
    * Make it easy to keep track of version details.
-   * 
+   *
    * @param {String} version
    * @param {Number} libraryId
    * @returns {_L1.Version}
@@ -103,19 +103,19 @@ var H5PUpgrades = H5PUpgrades || {};
   function Version(version, libraryId) {
     if (libraryId !== undefined) {
       version = info.versions[libraryId];
-      
+
       // Public
       this.libraryId = libraryId;
     }
     var versionSplit = version.split('.', 3);
-    
+
     // Public
     this.major = versionSplit[0];
     this.minor = versionSplit[1];
-    
+
     /**
      * Public. Custom string for this object.
-     * 
+     *
      * @returns {String}
      */
     this.toString = function () {
@@ -125,17 +125,17 @@ var H5PUpgrades = H5PUpgrades || {};
 
   /**
    * Displays a throbber in the status field.
-   *  
+   *
    * @param {String} msg
    * @returns {_L1.Throbber}
    */
   function Throbber(msg) {
     var $throbber = H5PUtils.throbber(msg);
     $container.html('').append($throbber);
-    
+
     /**
      * Makes it possible to set the progress.
-     * 
+     *
      * @param {String} progress
      */
     this.setProgress = function (progress) {
@@ -145,16 +145,16 @@ var H5PUpgrades = H5PUpgrades || {};
 
   /**
    * Start a new content upgrade.
-   * 
+   *
    * @param {Number} libraryId
    * @returns {_L1.ContentUpgrade}
    */
   function ContentUpgrade(libraryId) {
     var self = this;
-    
+
     // Get selected version
     self.version = new Version(null, libraryId);
-    
+
     // Create throbber with loading text and progress
     self.throbber = new Throbber(info.inProgress.replace('%ver', self.version));
 
@@ -164,36 +164,36 @@ var H5PUpgrades = H5PUpgrades || {};
       token: info.token
     });
   }
-  
+
   /**
    * Get the next batch and start processing it.
-   * 
+   *
    * @param {Object} outData
    */
   ContentUpgrade.prototype.nextBatch = function (outData) {
     var self = this;
-    
+
     $.post(info.infoUrl, outData, function (inData) {
       if (!(inData instanceof Object)) {
         // Print errors from backend
         return self.setStatus(inData);
-      } 
+      }
       if (inData.left === 0) {
         // Nothing left to process
         return self.setStatus(info.done);
       }
-      
+
       self.left = inData.left;
       self.token = inData.token;
-      
+
       // Start processing
       self.processBatch(inData.params);
     });
   };
-  
+
   /**
    * Set current status message.
-   * 
+   *
    * @param {String} msg
    */
   ContentUpgrade.prototype.setStatus = function (msg) {
@@ -202,28 +202,37 @@ var H5PUpgrades = H5PUpgrades || {};
 
   /**
    * Process the given parameters.
-   * 
+   *
    * @param {Object} parameters
    */
   ContentUpgrade.prototype.processBatch = function (parameters) {
     var self = this;
     var upgraded = {}; // Track upgraded params
-    
+
     var current = 0; // Track progress
     asyncSerial(parameters, function (id, params, next) {
-      
-      // Make params possible to work with
-      params = JSON.parse(params);
-      
+      try {
+        // Make params possible to work with
+        params = JSON.parse(params);
+        if (!(params instanceof Object)) {
+          throw true;
+        }
+      }
+      catch (event) {
+        return next(info.errorContent.replace('%id', id) + ' ' + info.errorParamsBroken);
+      }
+
       // Upgrade this content.
       self.upgrade(info.library.name, new Version(info.library.version), self.version, params, function (err, params) {
-        if (!err) {
-          upgraded[id] = JSON.stringify(params);
-
-          current++;
-          self.throbber.setProgress(Math.round((info.total - self.left + current) / (info.total / 100)) + ' %');
+        if (err) {
+          return next(info.errorContent.replace('%id', id) + ' ' + err);
         }
-        next(err);
+
+        upgraded[id] = JSON.stringify(params);
+
+        current++;
+        self.throbber.setProgress(Math.round((info.total - self.left + current) / (info.total / 100)) + ' %');
+        next();
       });
 
     }, function (err) {
@@ -240,10 +249,10 @@ var H5PUpgrades = H5PUpgrades || {};
       });
     });
   };
-  
+
   /**
    * Upgade the given content.
-   * 
+   *
    * @param {String} name
    * @param {Version} oldVersion
    * @param {Version} newVersion
@@ -253,19 +262,19 @@ var H5PUpgrades = H5PUpgrades || {};
    */
   ContentUpgrade.prototype.upgrade = function (name, oldVersion, newVersion, params, next) {
     var self = this;
-    
+
     // Load library details and upgrade routines
     self.loadLibrary(name, newVersion, function (err, library) {
       if (err) {
         return next(err);
       }
-      
+
       // Run upgrade routines on params
       self.processParams(library, oldVersion, newVersion, params, function (err, params) {
         if (err) {
           return next(err);
         }
-        
+
         // Check if any of the sub-libraries need upgrading
         asyncSerial(library.semantics, function (index, field, next) {
           self.processField(field, params[field.name], function (err, upgradedParams) {
@@ -280,24 +289,24 @@ var H5PUpgrades = H5PUpgrades || {};
       });
     });
   };
-  
+
   /**
    * Load library data needed for content upgrade.
-   * 
+   *
    * @param {String} name
    * @param {Version} version
    * @param {Function} next
    */
   ContentUpgrade.prototype.loadLibrary = function (name, version, next) {
     var self = this;
-    
+
     var key = name + '/' + version.major + '/' + version.minor;
     if (librariesCache[key] !== undefined) {
       // Library has been loaded before. Return cache.
       next(null, librariesCache[key]);
       return;
     }
-    
+
     $.ajax({
       dataType: 'json',
       cache: true,
@@ -306,7 +315,7 @@ var H5PUpgrades = H5PUpgrades || {};
       next(info.errorData.replace('%lib', name + ' ' + version));
     }).done(function (library) {
       librariesCache[key] = library;
-      
+
       if (library.upgradesScript) {
         self.loadScript(library.upgradesScript, function (err) {
           if (err) {
@@ -320,10 +329,10 @@ var H5PUpgrades = H5PUpgrades || {};
       }
     });
   };
-  
+
   /**
    * Load script with upgrade hooks.
-   * 
+   *
    * @param {String} url
    * @param {Function} next
    */
@@ -338,10 +347,10 @@ var H5PUpgrades = H5PUpgrades || {};
       next();
     });
   };
-  
+
   /**
    * Run upgrade hooks on params.
-   * 
+   *
    * @param {Object} library
    * @param {Version} oldVersion
    * @param {Version} newVersion
@@ -354,7 +363,7 @@ var H5PUpgrades = H5PUpgrades || {};
         // Upgrades script should be loaded so the upgrades should be here.
         return next(info.errorScript.replace('%lib', library.name + ' ' + newVersion));
       }
-      
+
       // No upgrades script. Move on
       return next(null, params);
     }
@@ -362,7 +371,7 @@ var H5PUpgrades = H5PUpgrades || {};
     // Run upgrade hooks. Start by going through major versions
     asyncSerial(H5PUpgrades[library.name], function (major, minors, nextMajor) {
       if (major < oldVersion.major || major > newVersion.major) {
-        // Older than the current version or newer than the selected 
+        // Older than the current version or newer than the selected
         nextMajor();
       }
       else {
@@ -374,14 +383,16 @@ var H5PUpgrades = H5PUpgrades || {};
           }
           else {
             // We found an upgrade hook, run it
-            if (upgrade.contentUpgrade !== undefined && typeof upgrade.contentUpgrade === 'function') {
-              upgrade.contentUpgrade(params, function (err, upgradedParams) {
+            var unnecessaryWrapper = (upgrade.contentUpgrade !== undefined ? upgrade.contentUpgrade : upgrade);
+
+            try {
+              unnecessaryWrapper(params, function (err, upgradedParams) {
                 params = upgradedParams;
                 nextMinor(err);
               });
             }
-            else {
-              nextMinor(info.errorScript.replace('%lib', library.name + ' ' + newVersion));
+            catch (err) {
+              next(err);
             }
           }
         }, nextMajor);
@@ -390,27 +401,27 @@ var H5PUpgrades = H5PUpgrades || {};
       next(err, params);
     });
   };
-  
+
   /**
    * Process parameter fields to find and upgrade sub-libraries.
-   * 
+   *
    * @param {Object} field
    * @param {Object} params
    * @param {Function} next
    */
   ContentUpgrade.prototype.processField = function (field, params, next) {
     var self = this;
-    
+
     if (params === undefined) {
       return next();
     }
-    
+
     switch (field.type) {
       case 'library':
         if (params.library === undefined || params.params === undefined) {
           return next();
         }
-        
+
         // Look for available upgrades
         var usedLib = params.library.split(' ', 2);
         for (var i = 0; i < field.options.length; i++) {
@@ -419,14 +430,14 @@ var H5PUpgrades = H5PUpgrades || {};
             if (availableLib[1] === usedLib[1]) {
               return next(); // Same version
             }
-            
+
             // We have different versions
             var usedVer = new Version(usedLib[1]);
             var availableVer = new Version(availableLib[1]);
             if (usedVer.major > availableVer.major || (usedVer.major === availableVer.major && usedVer.minor >= availableVer.minor)) {
               return next(); // Larger or same version that's available
             }
-            
+
             // A newer version is available, upgrade params
             return self.upgrade(availableLib[0], usedVer, availableVer, params.params, function (err, upgraded) {
               if (!err) {
@@ -484,4 +495,4 @@ var H5PUpgrades = H5PUpgrades || {};
     }
   };
 
-})(H5P.jQuery);
\ No newline at end of file
+})(H5P.jQuery);