BuddyPress.org

BuddyPress doesn’t use bb_users at all, only wp_users.

You have a standalone installation of bbPress which is where your users database is (because you mentioned bb_users, I expect)? Can we just clarify that you’ve installed WordPress, and activated BuddyPress?

Have you integrated your standalone bbPress install at all? If so, how? Via the “Use an existing bbPress installation” button in the BuddyPress Forums Setup page?