There are several possibilities, but I shall only touch on the two I know.
If this is a new problem and both the hardware and k3b were working before, it could be a hardware problem. Even relatively new disc burners can develop problems. The one one in my lap-top was fried after about only two years.
If this is a new installation, the problem could be with k3b. Myself, I always use xfburn. It is the most reliable burning application I have used. So you could try another burning application to see if the problem persists.
There is also the possibility that you will need to install a missing package, but that answer will need to wait for someone more knowledgeable.