I've had this many times in the past, specially with Facebook, kept telling me I'd changed my password and do I remember doing it. It's normally sorted itself out within a day or two.
But MicroB does go round the tank once in a while for me, not sure why, but I'm guessing it's probably dodgy cookies or a corrupt file in the browser history or cache.

Try clearing all your private data but leave Saved passwords unchecked.