I was logged in before such hour, but right now I tried to sign off and found a wrong certificate error that is nos preventing me to sign in again
I experience this from time to time. To fix it, clear all cookies (or the cookies that are specifically at google/gmail). It will then work.
Yeah!! It's working as usual for me. May be there's some problem with your browser's cookie handling or HTTP Request Sending.
I have been using Gmail for years and never experienced a problem. I think it is specific to your account. Hope you get/got it sorted!