When I try to add a domain user to the local administrators group, I receive an error saying that the user is already a member of the administrators group. The thing is, that user is not in the member list of the administrators group. Why do I receive that message.
I did a copy of the problematic user in the Active Directory and I am able to add that "testuser" to the local administrators group without any problem.
From my point of view, the problem is not related to user's permissions because I did an exact copy of that user and I can add that "testuser" in the group.
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