HotFix Certificate Failure

I have 3 Win2K DC’s that I cannot install HotFixes on. The error is “Digital Signature Not Found” followed by “The form specified for the subject is not one supported or known by the specified trust provider”.
I have checked all policies (local, domain and DC) and the driver signing restictions are not in place. I can run these updates on Pro and member servers but not the DC’s. I also get this error on the DC’s when I try to update IE to 6.0 from CD. I have scoured the Technet site and have run out of ideas. Can anyone please help, I’d really like to patch my servers!

Thank you.