An Error Ocurred Authenticating Your Request: A user with this email address already exists.

Hello everybody.

One existing user started to get this error recently, when he switches to Community via link from our member site.

He was able to get to Community previously with no problems.

Nothing weird in his Community User settings.

We are on v10.6 and use SSO plugin to authenticate.  

Any ideas?

Thanks, Vitaliy.

Clarified that this is existing user.
[edited by: Vitaliy Grabchenko at 5:56 PM (GMT 0) on Thu, Dec 9 2021]