Well, I seem to have sorted out all other problems, but I still can't get the PHP Accelerator to work for some reason. Whenever I turn it on, every forum/topic page you go to, it forwards you right back to ultimatebb.cgi. I checked the cache folder, and it doesn't seem to be doing anything there at all when the Accelerator is on. The board is functioning fine with the Accelerator off. Also, the Accelerator test shows everything being OK.
So this is rather baffling... it all worked ok before we moved the boards, but this new system has a newer version of everything, so I don't know if that could be a problem somehow. But everything else on the server is completely unproblematic. Any ideas?