Hey guys sound issue

Ok ladies and getns
How would i attach in a sound from an externally loaded sound. I had a method which i think will work. BUT i dont know if this is a bug with macromedia flash but i have lthis code

var my_sound:Sound = new Sound();
my_sound.attachSound("song", 99);

but it wont play. any ideas, and yes, i put the sound in the swf w/out loading externally to test this. and i think there lies my issue, because the exact same code works perfect in another swf