Is it possible that, somehow, this site got blocked (you know how sometimes the block messages pop up at the top and you accidentally hit them. Well, at least I do
Check in options/security. Also clear out all your private data, which you can do from the options as well. That'll dump your session info/cookies and any other possibly bad stuff. Also, if you're using firefox to save your passwords and you have that setup for this site, clear it out and then re-add it.
Hope something in there helped!