bbPress.org

If this is shared hosting, I think it’s overloaded. If it’s your own box, you can do something like this to see how many files are open:

ulimit -a

There are many reasons for too many open files, but I don’t think it’s related to bbPress since 0.9.x is pretty stable and I have not seen this error reported for it before.

If you post a link to your domain, someone can check and see how many virtual hosts are living there. Maybe one is just behaving badly.