Itunes Problem

My sister re-formatted her computer this week. Not sure if this had anything to do with the problem I had. I tried to burn a cd from my Itunes on her computer and when it began to initialize the burning, my cd popped back out and a message came up saying something like, "One or more of the songs listed is not authorized for use on this machine" ?? Does anyone know what this is and how I can correct it? Thanks.