If you updated MK8 to the latest version that came out a few weeks ago. CTGP-Cafe (and any other MK8 mods based on it) will no longer work. For the time being, in order to use such mods, you'll have to downgrade MK8 to its previous version. I've never had to downgrade a Wii U game, but there is a method here somewhere on how to do it, so it is possible.