Hi James,
I tried "Run as Administrator" (UAC is off anyway) before but it leading to the same error message.
Running gpresult -v shows me the following Groups that the Administrator is in:
None
Everyone
Local account and member of Administrators group
BUILTIN\Administrators
BUILTIN\Users
REMOTE INTERACTIVE LOGON
NT AUTHORITY\INTERACTIVE
NT AUTHORITY\Authenticated Users
This Organization
Local account
LOCAL
NTLM Authentication
High Mandatory Level