This is a part of a code from the jQuery library, to be specific this part is responsible for handling callbacks. It is displayed, because the reponse from wordpres is unparsable JSON data. If you try to regenerate the thumbnails again in firefox you can open the network tool from the developer tools and read the response from wordpress. In my case it was: `
Warning: copy(/var/app/current/wp-content/uploads/2014/11/reindeer.jpg): failed to open stream: No such file or directory in /var/app/current/wp-admin/includes/class-wp-filesystem-direct.php on line 231
{“error”:””reindeer” (ID 5149) failed to resize. The error message was: The originally uploaded image file cannot be found at <code>http:\/\/mysite.com\/wp-content\/uploads\/2014\/11\/reindeer.jpg<\/code>”}`
From there you need to figure out what to do, depending on the error message.
