Vista - Event ID 1058 - non-fatal exception

Hi,
I'm having a problem with a couple of my VM's which cause an error when I
try to shut them down. When a machine is switched off from within the OS
(i.e. rather than pulling the plug through the VS Web interface) it either
crashes or, in some circumstances, causes the VM status to lock on 'Turning
off' and prevents access to all the other VM's which are currently running on
the VS. This is a production system so that has caused some upset to the
users(!).

For reference, they client VM's are Windows XP SP2 and had not caused any
problems before we migrated the VS host from VS2005 SP1 on 32bit Windows 2003
R2 to VS2005 R2 on 64bit Windows 2008.

I have a very long (38KB) VSCrashLog<ddhhmmssmmm>.txt in
C:\ProgramData\Microsoft\Virtual Server\Crash Logs but it seems to mainly
contain a memory dump which doesn't mean a great deal to me.

Any help would be appreciated,
Andy