Attempting to restore true Administator privileges to the Admin account

Hi Everyone,

I am using a Windows 7 client on a Windows Server 2008 R2 Domain (and I am the Administrator of the Domain). The client that I am using is refusing to let me add addition User Accounts to the Administrator group (despite the fact that I am logged on as the Domain Administrator).





Furthermore if I attempt to log onto the client computer as the local Administrator by specifying the computer name rather than the Domain name at logon I see the following -



Finally if I then follow, these http://www.howtogeek.com/howto/windo...windows-vista/
instructions to enable the hidden administrator account I am met with the following message -



I have considered an offline password reset disk, however the local ('hidden') Administrator account is disabled! This feels like a catch 22, can anybody offer any suggestions on how to restore true Administrative access?

Any help will be greatly appreciated.

Kind Regards,

Davo