Post-SP1 VSS System Writer CAPI2 errors

Despite the fact that System Writer is missing from "vssadmin list
writers", System Restore points are successfully created and non-system
file Shadow Copies are also being created.

However, the most recent attempt to restore one of these points failed
without explanation. Fortunately, I image the partitions weekly with
Norton Save & Restore.

The other 6 Writers are functioning normally.

The following Application Log error is generated every time "vssadmin
list writers" is executed on Vista Ultimate.

Source: CAPI2

Event ID: 513

Cryptographic Services failed while processing the OnIdentity()
call in the System
Writer Object.

Details:
AddCoreCsiFiles : RtlConvertNtFilePathToWin32Path() failed.

System Error:
0xC0000039 (unresolvable).

%systemdrive%\Windows\Registration ACLs are correct per
http://technet2.microsoft.com/window...ed4551033.mspx

Thanks in advance.