BuddyPress.org

Make sure that bp is installed in a directory called /plugins/buddypress

Make sure that you are using the wpmu svn 2.7 branch http://svn.automattic.com/wordpress-mu/branches/2.7 not the wpmu trunk.

For some reason bp is not loading correctly. bp should be installed in the above directory and there should be other subdirs underneath that with all the components. Do you have this file in this path? /plugins/buddypress/bp-groups/bp-groups-templatetags.php

That is one of the files that is not loading.