update causes Virtual PC to stop working

After automatic updates, cannot start Virtual PC.
Error message: "the Virtual Machine Monitor driver required by Virtual PC
is missing. Please reinstall Virtual PC and try again."

The list of updates follows. More testing next time, PLEASE.

Status Type Date Installed
Update for Windows Vista for >64-based Systems (K8936824) Successful
Recommended 5/23/2007
Definition Update for Windows Defender - KB915597 (Definition 118.25493)
Successful Important 5/22/2007
MSXML 4.0 SP2 Security Update (KB927978) Successful Important 5/18/2007
Definition Update for Windows Defender - KB915597 (Definition 1.18.2547.1)
Successful Important 5118/2007
Update for Windows Vista for t4-based Systems (KB931174) Successful
Recommended 5/16/2007
Definition Update for Windows Defender - KB15597 (Definition 118.2544.4)
Successful Important 5/16/2007
Cumulative Security Update for Internet Explorer 7 in Windows Vista
x64-based Systems (KB931768) Successful Important 5/15/2007
Update for Windows Mail Junk E-mail Filterforx64-based Systems [May2007]
(KB905866) Successful Recommended 5115/2007
Update for Windows Vista for >64-based Systems (KB931099) Successful
Recommended 5115/2007
Update for Windows Vista for >64-based Systems (KB929685) Successful
Recommended 5/15/2007
Definition Update for Windows Defender - KB915597 (Definition 118.2540.1)
Successful Important 5115/2007