McAfee Virus Scan 2005 v. 9.0.

I just recently installed McAfee Virus Scan 2005 v. 9.0 (from store bought CD) on my old Dimension 4100 (Windows ME)  (replacing Norton AV which I previously had on the machine; the Norton AV was completely uninstalled before installing the McAfee AV.).  The McAfee seems to work OK, with one major exception.  The exception involves the automatic download / installation of virus definition updates.  The download part of the automatic update runs OK.  However, the installaltion part of the automatic update causes a "mini crash", i.e., the computer "shuts down", and I get the "scan disk running" notice due to "unauthorized shutdown", then the computer re-starts.  The installed definition update "takes" OK, but it causes that "unauthorized shutdown".  The same "unathorized shutdown" has happened with the last three or four automatic updates.  I have contacted McAfee on each occasion; they have been of no help.  Any ideas on what might be wrong?  Is McAfee Virus Scan 2005 v.9.0 really compatible with Windows ME (I mention this because I have a somewhat older version of McAfee on my 4600 which runs on XP, and no problems whatsoever).