I've got the same problem.
I went to cPanel and found that one part of the database was throwing up an error, so I changed the database type and checked/repaired it.
No dice.
So I moved all the forum files into a new directory.
Still no luck.
Finally, I've tried deleting the .htaccess file.
STILL doesn't work.
Any ideas?
EDIT: The URLs are http://www.teamsnafu.org/forums/ (old) and http://www.teamsnafu.org/forum/ (new).