Several Windows Updates Fail to Install

I think this might be a Group Policy problem that is blocking these installs.
I have several systems (mix of Windows XP professional and Windows 2000
servers) that will not install several pre-SP2 updates. One of the Windows XP
systems in particular will not install the updates for: KB842773, KB840315,
KB841873, KB839643, KB840374, and KB835732.

I tried downloading the updates and manually installing them in safe mode as
the local administrator and for all but KB835732 i received this error
message:

"Setup Error: You do not have permission to update Windows XP. Please
contact your system administrator." When I tried installing KB835732 I
received this error message: "Setup could not backup registry key
HKLM\SYSTEM\CurrentControlSet\Control\Nls\MUILangu ages\RC\rtcdll.dll to file
C:\Windows\$NtUninstallKB835732$\reg00003. 1314: A required privilege is not
held by the client."

The only systems I can apply these updates to successfully are not members
of our AD domain which leads me to believe its a group-policy issue but I
have no idea which specific security setting coud be causing this.