Yes, we had a configuration error on our end that caused an incorrect 'certificate revoked' error for people running Internet Explorer on Windows XP. (Technically, we had our server set to use SNI, a system that Internet Explorer on Windows XP doesn't support.) There's nothing wrong with our certificate, it was just a glitch that IE wasn't sure how to handle.
We fixed things up on this end once we figured that out and we should be all set going forward. Sorry about the hassle.