I use a child theme derived from the default team, only changing the visibility of the menu as explained in //http://buddypress.org/support/topic/resolved-hiding-navigation-links-for-buddypress-pages-for-non-registered-users/
When I use the default theme as such, it still doesn’t work.
I also tried to change the user’s role to author; still no luck…
Similar problem here: WP 3.5.1 multisite + BP 1.7.1
When admin accepts membership requests all works well; new members are added to the group list. But the new member doesn’t actually get access and still gets a message that says “this is a private group, request memberhip”.
I also use the DB Cache Reloaded Fix plugin.