[ERR] User 'xxx.yyy@xxxx.cz' had once existed and was deleted from the portal

What does it mean when the following error pops up? 

[ERR] User 'xxx.yyy@xxxx.cz' had once existed and was deleted from the portal. If you need to restore him, contact the portal administrator please.

The error occurs if the user is deleted only in the Infoport and Active Directory is trying to synchronize the user.

We recommend deleting the user directly in the Infoport database.