Bit more info - I have music playing in channel 1 - I enter a "game over" scene - I stop the music in channel 1 before entering the "game over" scene, then in the "game over" scene, I start a new music file in channel 1, which will not play at all.
But, in the game over scene there's a "try again" button, which if you click takes you back to the scene before the first music file plays in channel 1 - so if we enter the scene again where we first start playing music in channel 1, then it plays without a problem (the "game over" scene still doesn't work though).
Soooo, we're doing the same thing - stopping the music twice - but it will play the file it was already playing, but not a new one. That seems to be the issue.