Were you trying to delete something from your Watch List or Summary at the time? Did the message say something about having successfully listed "Spam and eggs from a cow's perspective"?
That odd message seems to pop up from time to time. As far as I can tell, it is just an odd error message that someone hard-coded somewhere that occasionally surfaces for no good reason, and it does not really mean anything.
I found some old references to it on the ebay.com community boards, but unfortunately the original threads with pictures of the error message have been archived or deleted.
