Music CD players are generally not designed to playback CD-RW/CD-R media.
Music CD players are manufactured for the purpose of playing back commercially available music CDs (pressed as music CDs). Optical pickups installed in these players are manufactured and adjusted to achieve their best performance in playing back music CDs.
Except for a small number of players released recently, music CD players cannot playback CD-RW media that are substantially different in optical characteristics such as reflection rate from those of music CDs. CD-R media, on the other hand, are not as different from music CDs in their optical characteristics as compared to CD-RW media. Yet some players cannot read them at all or fail to read them sometimes. Such inability and/or failure of reading of CD-RW/R media resulted from the specifications of music CD players.
Music CD players that are not clearly stated as "CD-RW/CD-R media playable" on their catalogs or instruction manuals may not be able to play them back or even if they can, their capability may not be guaranteed.