BuddyPress.org

It looks like there is specific code in wordpress since 2.7 to address this, but it isn’t working for some reason.

http://lists.automattic.com/pipermail/wpmu-trac/2009-February/002772.html

This thread is similar:

https://buddypress.org/forums/topic/404-page-when-trying-to-create-a-group-forum