Don't see anything that stands out. Do you have zlib compression enabled in the control panel? I was working on a site a couple days ago that was getting the same thing with zlib compression enabled. Wasn't just the forums, but other php pages that used it had the same thing.
So, there problem was something with zlib, once they disabled it, it was fine. Host is checking into it now. You might try disabling it and seeing if you still get blank pages.
