User has changed business units and is now unable to log in

User has changed business units and is now unable to log in

We had a user setup on one business unit and he has moved to a different one. We deleted him from the support reps and contacts of the old business unit and added him to the new. He is now unable to log in at all. I have tried resetting the password, enabling AD credentials (like we use for all other reps), and many combinations of removing and reading the user. All have provided no results. I went as far as to disable another working user to ensure we had not reached our license threshold. Any advice on what can be done to get this user in would be much appreciated.

Thank you,

Chris