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Fragment of a discussion from Project:Support desk
First of all don't use $wgMessageCache->addMessages() (ever. It will break in 1.18, and it wasn't meant to be used like that at really any point).
Second, you shouldn't be requre_once'ing any mediawiki files (mediawiki does that for you)
Third, your special page should have its own class that subclasses SpecialPage (It shouldn't be done via new SpecialPage).
See Manual:Special_pages#Basic_special_page_template for the proper way to do it (Mostly just the Basic special page template part of that page. The rest of that page is really rambely and not all that well written).
