I'm not working as a mod, but...
This might give you some ideas:
http://www.getnetgoing.com/HTTP-400.html
if what you're getting is a 400 error. There are some suggestions to try to fix the problem.
I've been noticing the site get awfully slow today, and I do note footnote 1 of that page says "The exception is that some proxies issue HTTP 400 after they timeout." It's possible that might be the cause. I've been getting the occasional message from Firefox saying that the connection was reset. Haven't seen any 400 errors. Yet, anyway.
Good luck!
Cheers,
bcg