I recently had a problem with NextGEN Gallery displaying images with the Thickbox option. I just started happening with no rhyme or reason and I was a little baffled for a while. There are several other threads like this one that might resolve your problem but it didn't help me.
The solution for me was simply a conflict with another plugin. So if you find yourself having this problem you'll need to go through your existing plugins and determine which one was the most recently added and turn it off. Simple.
Works fine for me now here: http://www.sanctuarymg.com/website-design-portfolio/