I never could get wpmu to run on top of bbpress. Evertime I tried wpmu would think I wanted to create a blog named boards instead of load the installation of bbpress in the directory called boards. (If anyone has a solution for that PLEASE point me in the right direction)
My friend (atomAstro on here) figured this out. In your wpmu-settings.php
file you need to add some code around line 119.
This:
if( $blogname == 'bbpress' ){
return true;
}
Should be added right above this:
if( is_array( $pages ) == false )
return false;
Change $blogname = ‘bbpress’ to whatever your bbPress directory is called.