I just installed MSM 2.0.
I was able to create a new site, assign the name, short name and description. I left all the “Move Data” options at the defaults.
After this, I could see the new site as an option in the upper-right, but I couldn’t select it. So I logged out. I had not progressed to the point of setting up my domain with the new site.
Now, I can’t log back in to my Control Panel at all. I don’t get any error when I submit the login.