Moe,
I am currently going through the same problems with my elkhorn but with musket caps. I bought a new nipple and it fired twice and then I experienced the same problem. I contacted CVA and the tech. said to run a piece of emery cloth around the nipple and the try it. After using the emery cloth it fired the caps with no problem. I'm headed back to the range in the morning to try it again.
Good luck