For some unknown reason when you want to choose the custom skin template and choose any skin from 32x32, 64x64 and even 128x128 size and it goes back to the game, then the game says: "that's not a Minecraft skin, silly.", even though it's the right pixel size and is in the way a skin template should be. Then after that it just goes gray and doesn't allow to touch the "choose new skin" that way.