Expected version of the product was not found

For the past year, I have been updating the Junk Mail filter on a
small LAN (about 15 workstations) without any problems.
They are all XP PRO sp2.
Last month, with the September 2007 (KB936677) update, 3 of the
workstations displayed 'Expected version of the product was not found
on your system.'
All updates were installed as Admin.

All assistance is appreciated.