If this is still a problem, then you can find my answer on wordpress.org’s support forum, it might help: wordpress.org/support/topic/resize-failure-on-some-images-with-odd-message
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.