Could not log in on the main message board/forum page. Would click the link and nothing pops up. Was able to log in from Blackhawks forum. Temporary glitch?
The only explanation I can think of, is the updated jquery and the jquery in your cache were mismatched. Because that's the only change made over the last few weeks.
So you may need to clear your cache if it still happens, and/or delete the CCS cookie from your browser and try again.
Edit: OK logged out, cleaned brower cache, cookies, history ect.... closed borwser, restarted it. Same problem. I'm at work, might be the system security.
I synced up some of the files that weren't 100% matching on our end(just legacy ie6 templates). The fact that you say one theme works and another doesn't is why I think this could also happen to other users. I just haven't been able to recreate it.
If the problem persists, what browser are you using?