BuddyPress.org

@Mohit Kumar: I know this has to do with cookie integration but I have found that sometimes the buddybar doesn’t work if this code isn’t in your bb-config.php file if you are using WPMU 2.7.1:

//WordPress MU Cookie Integration

define( 'WP_AUTH_COOKIE_VERSION', 1 );

If you could also post you WPMU wp-config.php file without the passwords and usernames it would be helpful as well.

@Nicholaszen: When I made that upgrade, I ended up having the same problem. I moved all of the plugins from /my-plugins/ to /bb-plugins/ and the themes from /my-themes/ to /bb-themes/. That managed to reset the site enough so that I could access the forum’s admin and from there I could re-activate the theme. Try that and let us know.