I actually got that once. Don't remember what I was doing, but it scared the crap out of me because I'm one of those where Murphy's Law about "If something can go wrong, it will" happens all to often. So I rebooted, held my breath and never saw it again. Popped open a few cold ones after that.
Ya know the real funny thing is that after I installed the program and had like 5 or 6 screens to cycle randomly, this was the first to come up and the dang puter CRASH! .. TWICE! LOL, had to do a rollback. o_O
.. that'll learn me.