Thanks again for letting me hunt down the problem on your server, DiscoBiscuit.
The problem was that a file was removed from SVN, but was still left on DiscoBiscuit's server. I forgot to remove the include statement for the file that was removed, so it was still being loaded for his clients... which ended very poorly. Now that the latest revision has the include statement removed though, it doesn't matter if the file still exists on people's servers anymore.