The second, which danbuter experienced, sends you to your profile page. We've recently reproduced the problem, but are only able to do so by logging in using the "reply" link, then clicking one of the other reply links on the page. While we prepare a fix for that issue, you should be able to work around it by refreshing the page.
Danbuter, does this sound at all like the circumstances you encountered?
i had that happen to me recently....tried logging off and on...clearing my cache..
it just started working again after about an hour and half or so..
i was logged in and had replied before it happened...went afk for a little while..came back and it wouldnt reply...
dont know what it was...