Buddypress Cannot Create Forum Topic

Maybe this is the core problem of Buddypress, but I wonder is anyone experiencing the same problem as I do? Or maybe this is a theme problem. When I try to post a topic for a forum as a test user, I got the error says - there was a error when creating a topic. And so no topic got created!

I know my setting is very OK, because I use one click install of Buddypress's BBPress integration. And so I didn't stray away from the recommend default setting. Using Buddypress 1.1.2, and wordpress mu 2.8.5.2. Using multidb (latest). Using bp-corporate theme.