That would be /index.php?title=MediaWiki:Noarticletext (which you can easily get at via /index.php?title=Special:Specialpages and search for the string, "There is currently no text...," but it's not really a 404 message - its a wiki message. I think you have to have server tinker-tailor-soldier-spy access rights to customize the pages thrown by the server. Stabatha Cogsprocket wrote:

Sounds like a mistake in however you've done the short URLs - certain urls (ones with extra slashes, perhaps?) aren't getting passed to index.php. If you give the details of how you did the short urls (copy and paste the code you added and say what file(s) it's in) we might be able to help.