Raspewtin, you got it right. Since CDRs use a dye that can only be burned away once, if something goes wrong in supplying the data fast enough to the burner, the CD can't be continued written to (unless your burner has BURNproof, JustLink, or other "absolute position recording" techniques for restarting where the laser left off), thereby rendering the disc uselss, also known as a coaster. CDRWs can simply erase the data and start over again though, so you can't get coasters on CDRWs 🙂