So, I have the same problem as reported in this thread: http://wordpress.org/support/topic/plugin-wp-ajax-edit-comments-not-popup-please
The thing is, I'm kind of a newbie and don't understand how the problem was solved.
Sometime ago the WP Ajax Edit Comments and the NextGen Gallery thickbox always worked, but then, it stopped working, openning images or the comment edit in a full page. Since it happens with both plugins, I imagine the problem may be with my theme, but I don't know how to solve it.
Can anybody help me?