This past week, I've made 3 batches of Merken's white choc candy clay that have crumbled upon kneading. I do 1lb of chocolate per 1/3 cup of corn syrup. This does not happen with the Merkens milk chocolate batch. What is going?

AHow are you storing it when its finished? I made the mistake of not covering it well and it dried out making it impossible to use.

The only other thing I can think of besides that is over mixing.