Since I have one of those myself, this post peaked my interest.
Doing a google search I gather that unless the tip your firing pin is damaged causing a sharp point the pin isn't puncturing the primer. So check to see if your pin is sharp first.
The next issue I found was your spring not being strong enough. I'll quote the post I found.
So check to see if there are little discs in your bolt.
In case you haven't taken your bolt apart before...
I don't think your firing pin can be too long all of a sudden unless there is some damage to the beefier parts of it. While your bolt is apart look for any signs of damage.
(Might as well do some maintenance while you have it apart.)
Basic Rifle Maintenance - Part 1
By Vince Bottomley
It may be the ammo? I know I have never had any sort of problem with mine, try some different ammo if you don't find any other problem.
More info is always helpful.
Was it just two rounds of did you shoot more beforehand that were ok?
How long was it since you last shot it?
Do you keep it cocked while storing? (I let my spring relax.)
I hope you figure it out.