Disable the “Other people are logged on to this computer” message on a Windows VM

If you’re logged on with Remote Desktop (and probably in several other cases) Windows will not respond appropriately to the power button being pressed. Instead of shutting down, it will display a message asking you if that’s what you really want to do, as if holding the same button for 5 seconds to force the damn thing to shut down isn’t your next move.

This solution may or may not be Windows XP specific, as that’s where I encountered the issue, but I’ve confirmed that setting the following registry key removes this message and shuts down when a simulated ACPI button is pressed:

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Error Message Instrument]
"EnableDefaultReply"=dword:00000001