bbPress.org

If you have done the following:
– disable ALL plugins one by one (not just ones you think could be causing it)
– activated a default theme
– used the repair tools
– re-saved permalinks

And it’s still broken, then the only next thing you can do is create a local installation of bbPress and test the reverse way, test it’s working, add your theme, test it’s working, add one plugin and keep going till it breaks.

Good luck with your site.