I think Mercury receives the medal for the least informative error messages. There's the infamous WinRunner "General Error". I think the following error takes the cake, however. This was shown to me by a co-worker trying to connect to Quality Center. It was very hard not to laugh:
Some time ago, one of the PC magazines used to have a page of sardonic humor at the end. And one regular feature was "interesting" error windows. My favorite was one that began something like "Twain error" and ended "Big trouble. We're going to die."
The shortest I recall just contained "!" in the text area.
I remember one in Norton Utilities 5.0 (Disk Doctor to be precise) that we removed last minute. It occurred when NDD found a spanned partition onto a IOmega HardCard (remember that thing?). Because of the way the I/O of the HardCard was being handled it caused NDD to barf. So we put in an error trap and message.
The developer forgot to put in the proper error message on one of the last builds. His temporary message was "Dude, you're screwed. I can't handle this!". Which we caught in the last round of testing and had him change it to "Norton Disk Doctor does not support spanned partitions across IOmega HardCards".
Imagine the first customer calling in to support saying they got the "Dude you're screwed" error message.