its required on ClanBase that you have no custom pk3s in your main folder. If you are caught with any custom pk3s the opposing clan can force your clan to forfiet the match.
you can download this little program for MOH:AA which removes all your custom pk3s with a click of the button, then when the match is over it restores your custom pk3s with a click of the button
http://www.rootme.nl/~pandora/files/customfilemover.zip