BuddyPress.org

korhanekinci, yes, I did add those four lines that the bbPress Integration plugin suggested.

I also defined WP_AUTH_COOKIE_VERSION. Without this line the cookie integration doesn’t work at all.

Like I mentioned above, my current clue is that only users who have NO caps in their “login_name” (field in the wp_users table) can post on the forum.

Now, WPMU strips caps from the username when people register, but I have bbPress users that pre-dated the WPMU integration and they do have caps in their login_name.

One other datapoint to add: I tried a standalone installation of bbPress 1.0.1 and it doesn’t have this problem. Users with caps in “login-name” can post fine.