Fatal error ( Blogs MU ).

I did just install Blogs MU, buddypress and membership and now i have this fatal error on my frontpage :

Fatal error: Call to undefined function groups_get_total_group_count() in /home/sorgogmi/public_html/wp-content/themes/blogs-mu/lib/templates/wp-template/sections.php on line 21

Any ideas how i can fix this fatal error ??