When I committed, I was asked to enter my name and my email. Even though I used the same email address that I used for all other StackExchange accounts, it wasn't able to recognize me. This is a bug in Area51. Below I explain a strategy to reduce the chance of this happening, and a solution if it does happen:
First sign into StackExchange: https://...
I used my Google account to create my user i was able to see my profile has unregistered and i wasn't able to login.
To fix it I use an anonymous tab in chrome and registered my user again, then i re login and was able login.
Probably a cookie that created an inconsistency in the system
This morning, another user had exactly the same problem with exactly the same error message (sharing with his permission):
He eventually got it working by switching from Firefox to Chrome:
It's very strange though, that by doing this his 3-month old account (see above screenshot) was replaced by a new account active "since today", and the new account was ...