Neil McDonald's Dynamics 365 and Power Platform Blog

One of our users had complained that their name was spelled incorrectly. I made the changes in AD, Exchange and in her CRM user account, but when I tried to change her domain login name in CRM, I received the error ‘You are attempting to create a user with a domain logon that is already used by another user…’

To get around it, I made the change directly in the organisation database. The domain login name is stored in the ‘DomainName’ column of the ‘SystemUserBase’ table, so I just edited the data within SQL management studio.

FYI – Although I do this, I don’t recommend making any changes to the CRM databases directly. A safer workaround is posted here