Hi there, had this happened with you just once or it is a repeatable every time you try to log in?
I've seen this happen to my account - just today. Turns out if you change password with google your openid changes as well, hence the prompt to create a new account.
Maybe there are other situations when google changes user's openid, if anyone knows more details - please share them.
There is no account recovery feature in askbot yet, but this is high on the list of priorities together with the proper account merge feature.
So for now please ask the user to register again, sorry for the inconvenience.