This template should use an internal link, not a link to "fileformats.archiveteam.org". Normally, you can link to a category page adding an initial colon ("[[:Category:Files...]]").
But when I preview such a change, it suggests the link is not valid. Maybe just a preview quirk? I'll probably try it anyway (and maybe make a mess of every page on this site). Jsummers (talk) 02:35, 1 March 2014 (UTC)