Quoted from wcbrandes:Yes this was my first though but after further investigation and taking apart the crypt the problem lies in the back of the skull behind where the spring is. There is a plastic end that slides up and down a metal brace and it has a little cut out it seems to catch on. Perhaps you mean it's catching back there because the skull isn't coming forward enough?
I think there's a few different possibilities where it can 'stick'. Can you post a pic of this 'cutout'?
Rob