Were you using a Lee collet sizing die? That has happened when I have used one, from time to time. If that's the case, you have a couple of choices. The first would be to contact Lee, get a new depriming rod, cut off the decapping pin and you're back in the sizing business. The second would be to make a new rod, sans the decapping pin if you have access to a lathe, or a friend who will make one for you.
