I added a Windows Server 2008 R2 x64 to my 2008 domain. When I attempted to add the domain admin to the local administrator group I got an error that it already is there!

But when logging in as the domain user I did not have admin rights. I kept seeing access is denied. This is what I had to do to resolve the issue.

1. Remove the account from the admin group via the command line using this command:

  net localgroup administrators domainname\userid /delete

2. Then going to start –> run and type: control userpasswords2

3. Click add.

4. Type in the username and domain.

5. Select Administrator

You are done! Hope this helps!