I seem to be experiencing a machine lockup when I use Windows XP Switch Users functionality. It’s happened twice now.
If I log into account A, then switch users to account B, then log out, the machine becomes unresponsive. Black screen, as if it has gone into sleep mode. Pressing Caps-lock doesn’t change the caps LED. The only option was to power cycle.
I notice the following event log entries:
“Windows cannot unload your classes registry file - it is still in use by other applications or services. The file will be unloaded when it is no longer in use.”
… 30 seconds later…
"Windows saved user HERGEST\Phil registry while an application or service was still using the registry during log off. The memory used by the user’s registry has not been freed. The registry will be unloaded when it is no longer in use.
This is often caused by services running as a user account, try configuring the services to run in either the LocalService or NetworkService account."
My guess is that the Comodo firewall is blocking some important system action during switch users/logoff. 