I think you have to patch the ISO to IOS249 and burn to disc. This game will not work on USB Loader. Check out this list of usb loader problem games, scroll down to "problem catagory 1 (IOS reloading games)", LOOK HERE. And, if you happen to backup Splinter Cell Double Agent, you must also patch the ISO to IOS249 and burn to disc.
Maybe this problem will be fixed on all IOS reloading games soon, they fix the new games but not the old games.
So that means if you are going to patch COD 3 to 249, then delete the save game from the Wii internal memory or risk bricking when you play the patched game.PS: If you played one of these games unpatched, and now you patch(IOS Version patch) it in order to get it to work, you might run into savegame problems. It's confirmed that if you play FarCry until the crash point with the unpatched disc and then play further with the patched disc that you get savegame bugs up to a "system files are corrupt" message. So if you read this because you were searching a fix for one of these games, delete the savegame or have good brick protection when you patch now!
Source - WiiPower at GBAtemp