Same problem here. Also, when clicking the Edit profile link, the page is blank, showing header and footer and everything but nothing inside, not even the little sidebar at the left with the avatar picture and the other links (Subscription, Topis started, etc.), all empty and not even present in the source code.
WP: 3.5.1
bbPress: 2.2.4
Using the Thesis Theme and s2Member plugin.
Solved the problem. Turns out I needed to install a compatibility plugin (provided by the Thesis Theme developers). I don’t know if I will be able now to properly change the forum font size, but everything else works perfectly now.
I hope this helps someone else with the same issue (i.e. anyone installen bbPress in a blog using Thesis), because I searched for this for days and didn’t find any answers, not here, not on the WP forums. The answer was in the private Thesis forum.