Standalone shutting down cleanly on Windows

[Ben Rubinstein]

I have a standalone that's supposed to perform various tasks when it exits.  I 
thought it was doing so, but having recently changed the hardware it's running 
on, there's now an error on shutting the machine down which we've traced to my 
app not doing these tasks.

The app consists of a mainstack and a sub-stack, but the sub-stack is only 
ever opened if the app is used interactively, which it generally isn't.

The app performs the shutdown tasks if it gets either a closeStack or shutDown 
message.  It currently logs things so I can find out what's happening.

- If I quit the app from its own menu, it gets the shutDown message, does its 
stuff, I can then shut down the machine without error.

- If I right click the button for the app in the taskbar, and select Close, it 
gets the closeStack message, does its stuff, I can then shut down the machine 
without error.

- If I shut down the computer from the Start menu (which is closest to what 
actually happens in production use) then the log doesn't show it getting 
either message.  So it doesn't clean up properly, and then Windows throws an 
error.

Is there another message I could be trapping?  Is there something else I need 
to make sure that one of these messages is sent when Windows shuts the app 
down?  Is there a trick I'm missing?

TIA,

Ben