Go over your wp-config and bb-config installs and make DAMN sure they’re talking to each other. Check the DB name and password. Go into your SQL db and make sure that bb_ and wp_ are in the same database. When you login, look at the cookies in your browser and see if anything jumps out about their similarities or differences. Triple check your KEYs and HASHes, and I’d even go so far as to reset them. Can’t hurt, can it?