Hey Paul,
One of the most difficult things to troubleshoot from my experience of managing domains.
Those two things I believe would be related through Single Sign on and domain security.
My best guess where to start would be logon scripts and group policy objects.
You can also see local event viewer logs from the computer and look for group policy related things.
It could also be a bad connection during logon causing the GPO to not map during the credentials being inserted.
Another thing to ensure is that the password and username is sync'd between the local users computer and the domain controller.
