MML isn't a regular SmileBASIC program. That is to say, you can't execute it. To play back that song, usually you would just read the file into a string array and tell BGMPLAY to play it. However, to keep things simple, you could surround your above code snippet with quotations and put BGMPLAY in front of it. Like this: BGMPLAY "{P0C0=@99......{P0C1}]" (the .... are just placeholders)