Re: wpmu/bbpress logins work, forums don’t!
Is there an .htaccess in the directory one level above? .htaccess rules are additive, I think. So if there is one in the directory one level up, those could be conflicting with the .htaccess you have in the community directory.
edit: sorry, I just reread all the notes you posted. I don’t understand enough about .htaccess to know what the problem is. SamBauers here has made several posts about .htaccess.