I upgraded the Forum today. I noticed there were a few problems logging in, I’m hoping it fixes the problem. If not, you should try logging in through the WordPress login. If you have problems or questions, e-mail me at firstname.lastname@example.org.
Ugh. Okay it seems even after the upgrade the problem persists. I’m sorry. Apparently one must delete their browser cookies (it’s under your options > privacy) once you do that you should be able to login in again.