BuddyPress.org

@Michael-

… I just updated to the latest trunk. Before I had 1303 installed…

What version of BuddyPress are you currently running? If it is 1303, that is not the latest trunk version. Try updating to the most recent trunk.

Also, did you add the one additional define line to WPMU’s wp-config.php file? If not, compare the 2.7.1 config file to your old one. This line is new:

define('SITE_ID_CURRENT_SITE', 1);

Since you can see the admin screen when you remove BP, that should not be the issue. But I’m just trying to be thorough.