Sansa Clip + : A 'single' MP3 doesn't download

Windows 10: I’ve downloaded well over a hundred MP3  from Amazon to my PC with NO difficulties but for some reason there is a single MP3 that does not download to my Sansa Clip+ (1 GB free space). I even tried downloading to the external drive on the Sansa Clip+ also but the MP3 jus won’t transfer…