I'm finishing a guitar. Why is the clear enamel crackling REALLY bad in some places?

The finish is looking awesome so far, but I'm getting frustrated because on the back and a few places on the sides the clear spray enamel is crackling up. It looks horrible and even after sanding and cleaning the surface, it still does it. Now, given this is cheap wal-mart enamel, but it still shouldn't be doing this! Please help! I don't mind switching the enamel if I have to, but wouldn't a different kind of enamel react to the enamel that's already on there? Thanks!