Minimalist error message
"Just keep on movin', folks. Nothing to see here. Really, this is all you need to know. Anything else would only confuse you."
This is a real error dialog from a real app. Not a beta release, either. And no, I didn't capture the screenshot before the dialog was fully rendered - this is the whole thing. (I did add the caption, though.)
So we're not only left to wonder what the error was, but also what application had the error in the first place. Huh.