Thrush is right but also sometimes it can be just the laser condition and age. If its an old appliance it could be very dirty and sometimes the old disk cleaner packs won't do. I had a similar issue and took the cd player apart got to the laser and wiped it fairly firmly with a clean dry cloth. Then it ran them.

But again if its a new unit or it won't play them from the start then its the RW disks.