Why is my game cube controller not working with my Wii?

I bought a Pelican, Flashback Gamer Pack, that included a controller for the game cube and a memory card. Got it at Wal-Mart. I found this out when I tried to play Blood Omen 2: Legacy of Cain. A pretty old game cube game, but still an awesome one. Is it the game, the controller, or something to do with the Wii? Please help. I really love the idea of the backwards compatibility of the Wii and have bought a ton of old game cube games, but this problem is stopping my dream of retro gaming on a next gen system from coming to fruition.