Check the time is correctly set on your machine =)

I am also seeing this error, and the time on my machine is set properly (it's actually controlled by a group policy). I'm curious if this is because I am accessing from work. My company uses firewalls and a proxy server, among other methods of security. However, I can still access GMail through IE. Is anybody having problems at home on a personal computer?

Did you retrieve and inspect that certificate to see if that brings any clues?