I ran into this same problem, because I'm styling my gallery to fit in with our web site. Then I fixed it! I thought I'd share what I did, just in case it helps other people.
It turns out I deleted a tag:
<div id="extrainfo"></div>
I put it back on the page, and it works again.
This is how it works:
- you click move/delete
- fancy JavaScript goes to the server to get the move/delete form
- the JavaScript puts that form inside that "extrainfo" div on the page
- voila! you have a move/delete form without having to leave the page you are on
In my case, it broke because I removed that div. So it's no surprise that putting it back fixed the problem.
Mary