BuddyPress.org

Hi,

review all site settings and check about the fatal error mentionned on the /register/page:
Fatal error: Call to undefined function groups_get_total_group_count() in .../wp-content/plugins/buddypress-registration-groups-1/includes/bp-registration-groups.php on line 53

I think that your buddypress-registration-groups plugin folder is malformed.
buddypress-registration-groups-1 is most probably written buddypress-registration-groups