Resin question

Okay so it seems that some of my resin has gone bad or I'm not mixing enough, because when I demolded a couple of claws they were almost jelly-like. They aren't sticky to the touch but they seem to be half cured or something. I can bend them back on themselves and they won't rip.

My question is: If anyone's come across this before, what exactly is causing it? And is there anything I can do to harden them?