I got this error message on my machine at work the other day. I don't really remember what I was doing at the time, and I know that the interaction between GUIs and underlying operating systems is complex. But I got a huge chuckle out of one interpretation (admittedly the most sarcastic, cynical one I can think of, but none of you should be surprised by this):
"To protect your computer, Windows has shutdown Windows."
My thoughts exactly.