Digital sound files must be organized and structured so that your media player can read them. It's just like being able to read and understand a different language. If the player "speaks" the language that the files are recorded in, it can reproduce the song and make beautiful music. If it can't speak the language, the numbers of the music don't add up, and you get an error message - and no music. Error messages are frustrating, but you have some defense against them if you understand the major audio file formats.