Administrators group rights in Server 2008

We have a Windows Server 2008 SP2 Standard 64-bit operating independently in workgroup mode, without Active Directory installed.
We want only members of the group "Administrators" have access to the partition D, so we changed the security permissions on this drive; now there are only three rules in the information security: the built-in group "Administrators" with full access to folder, subfolders and files, the built-in group "System", with full access to folder, subfolders and files, and the built-in group "Creator Owner" with full access to the subfolders and files. The owner of the D drive is also the group "Administrators". UAC is enabled for all users.
When we try to access the drive D, using an account of the group "Administrators", we received an access error and a message "Access Denied". The only way to access is to disable UAC for members of the group "Administrators", but we prefer to use UAC on the system for all users. Another way is to give access rights to each member of the group "Administrators" individually, but this is not a good solution.
We realize that giving access to other groups such as the built-in group "Everyone", solves the problem, but obviously we did not want to give everyone access to this unit. We thought if we gave a group of users full access to a resource, we were giving full access to all group members, but it seems that UAC is interfering with this basic behavior of the system.
Anybody know how to set permissions to give access only to members of the group "Administrators", without disabling UAC for the group "Administrators" or completely, and without giving permissions to each group member individually?