Error 1931 persists after Knol. Base Art. 274041 compliance

[Alex Smith]

Text from dialog box:
Error 1931. The Windows installer service cannot update
the system file C:\WINNT\System32\PSAPI.DLL because the
file is protected by Windows. You may need to update your
operating system for this program to work properly.

Reference Knowledge base (KB) article 274041: A Similar
message had formerly displayd except that VGX.DLL was
involved. This has been addressed by installing Internet
explorer ver 6 as cited in the KB but now the new
offending file is PSAPI.DLL.

Repair mode tried and then fill uninstall / reinstall
tried. Error message in all cases.

Any ideas?

Thank you,
Alex Smith