I’m using WP 3.5+
In my case when I click to the “Upload image” button, nothing happens and JavaScript error will be logged:
[00:58:32.348] ReferenceError: event is not defined @ /wp-content/plugins/wp-simple-galleries/wp-simple-gallery-admin.js?ver=1.34:41
Looks like the problem lies here:
event.preventDefault();
