Caveat: I haven't tested this on an online site, just on a localhost installation on my computer (I use Xampp as my Apache/MySQL environment), but I would imagine the behavior would be the same in a real-world scenario.
I saw this thread by Piotao and Juggledad, but my error was produced on a page, not a post. So no category would be applicable in this scenario. I'd hate to break something by applying patches I don't understand, would the solution on that page still be applicable?