SanDisk Sansa Clip+ having problems with playing songs as a player.

SanDisk MP3 players Sansa® Clip | Sansa® Clip+
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As long as you have copies of the music elsewhere, formatting the unit with its internal Format command (under Settings/System Settings) sometimes fixes peculiar behavior. You’d have to reload the music, of course. Might not help, but it’s worth a try.