I had the same thing happen to one of my users. Nothing seemed out of the ordinary. The night before, she had no problems logging in. Then the next morning, she got the same error. So I did do a user recovery and it works just fine. The only thing I can see from the logs was the previous night it looks like someone started a recovery but without the codes, they couldn't do anything.
I'm just wondering what could possibly cause this condition to occur?