[Plugin: NextGEN Gallery] Does not work

Thats usually theme related. THickbox almost always works for me..

Make sure wp_head() is in your theme’s header file. I had the same problem on my site, lightbox wasn’t working, but it says in the Codex that wp_head() is what plugins look for when they’re inserting scripts and whatnot, so I put it back into my header file and lightbox worked again.