So I logged out, and wasn't able to login again at all. I got the same error, both for trying google SSO, and for using a user/pwd.
Eventually, I just placed my user name in the login box, and a few hours after, the app popped up asking for a password, allowing me to login again.
It is as if there is a huge delay (a few hours) on the login request from the Mac App. This is really weird.