Forum Troubles

I have a problem. When I try to install a forum with bbpress in buddypress it say this: Warning: array_key_exists() [function.array-key-exists]: The first argument should be either a string or an integer in /home/studypee/sites/ on line 400

What is that? When I click on the forum menu it redirect me back to the frontpage.

My website is:

Hope you can help.