Like Dave I am having almost the same problems, but this is on a Server 2003
installation. I am running as the Schema Admin, which is also a domain and
enterprise admin. I get the same error whether running on a different server
or on the Schema Master itself.
I can no longer access local users as the Schema Master is an AD controller.
As a member of all three of the user groups, I certainly should be able to
access everything (in theory

)