"The Group Policy Client service failed to sign-in. Access is denied" error observed on login to servers after UPM profile migration.

Give permission to the user profile (NTUSER.DAT-it is found in c:\users\<username> as a hidden file).

1. Login to Windows with a working administration account.
2. Open registry and click on HKEY_USERS
3. Click File -> Load Hive..., select the affected user's NTUSER.DAT from profile store, Enter a temporary name.
4. Right click on the loaded hive with the name given in step 3 and select Permission.
5. Give Full Control permission to SYSTEM, Administrators and the affected user.
6. Click on the loaded hive and click File ->Unload Hive...

Problem Cause