Try using the sound class instead. That way, you can have the music start and
it will just keep on playing. First, open the library. Then right click on your
sound. Select Linkage... Then check off the box: Export for ActionScript. Then
type in mySound for the Identifier. Hit OK. Now, whenever you want to start
your sound, use this ActionScript:

theSound = new Sound();
theSound.attachSound("mySound");
theSound.start();