When I upgraded to WordPress 3.5, this plugin stopped working in my local environment. It still worked on my server, even though I have the exact same setup on them both. What's even more interesting is that it only failed the uploads when using AJAX.
So, after some investigation, I realized that the reason this is happening is because the image_resize function - being used by this plugin - has been deprecated in favor of wp_get_image_editor.
When doing an AJAX upload, the AJAX post returns JSON, which is then parsed by the JavaScript on the page. Being that I have WP_DEBUG turned on in my local setup, WordPress was emitting the following notice:
Notice: image_resize is deprecated since version 3.5! Use wp_get_image_editor() instead. in wp-includes/functions.php on line 2824
which originates from imsanity.php:112.
Since the notice is being echoed right there in the response, the returned data is not valid JSON, so it seems like an error.
