[Trent Adams]

Personally, I have had issues with this as well. I would suggest creating a .htaccess file and place it in your bbpress root directory and only adding the following to it:

Options +MultiViews

That seems to work for most people. Try that first maybe? If not, maybe check what format you have in your WP .htaccess and try a combination of either the previous code or what rewrite-rules.php spits out for you.

Thanks,

Trent