When trying to play music the display shows "Unknown Format"

This is true, common bitrate tho is 128 (standard/lame old) While highest quality last I knew was 320. I found high bit rate though is not always best have ruined songs and higher bitrate decreases the amount any mo3 can hold. For instant say common 2gb - 4000 songs well that is mainly dependant not on length but on bitrate being 128 increased to 192 is approx 3250 and 320 itrate is 2000. I have a Sansa c240 (bought in 2007) some songs at 320 either jitter or just wont play. but there is away to correct it fortunately. Solution is to use an audio converter you will need all format details to get 320 bitrate to play properly but that is so time consuming best just to lower the bitrate until find one that plays properly. This is true, common bitrate tho is 128 (standard/lame old) While highest quality last I knew was 320. I found high bit rate though is not always best have ruined songs and higher bitrate decreases the amount any mo3 can hold. For instant say common 2gb - 4000 songs well that is mainly dependant not on length but on bitrate being 128 increased to 192 is approx 3250 and 320 itrate is 2000. I have a Sansa c240 (bought in 2007) some songs at 320 either jitter or just wont play. but there is away to correct it fortunately. Solution is to use an audio converter you will need all format details to get 320 bitrate to play properly but that is so time consuming best just to lower the bitrate until find one that plays properly.