NTVDM CPU has encountered an illegal instruction.

From: *** (anonymous_at_discussions.microsoft.com)
Date: 09/30/04 

Date: Thu, 30 Sep 2004 01:31:33 -0700

I get the following pop-up box at start-up now. I have
just installed XP Home service pack 2 to try and get rid
of the pesky pop-up to no avail.
______________________________________________________
16 bit MS-DOS SubSystem
______________________________________________________

C:\Progra~1\COMMON~1\updmgr.exe
The NTVDM CPU has encountered an illegal instruction.
CS:0f79 ip:001d OP:ff ff ff ff ff Choose 'close' to
terminate the application.

Close Ignore
______________________________________________________

If you click either 'close' or 'ignore' it disappears and
the computer works OK (though am I imagining it now runs
slower???) until the next log on when it appears again.

How do I get rid of it?