when I relauch my game the background music is gone

I've made a little game with a short .aif background music track which works perfectly. The audio is attached to the main camera it plays on wake and loops. If I click the home button on my iphone the game is put in the background. When I click the game icon again I'm back in the game but the music doesn't play any longer - what am I doing wrong?

Thanks Jeppe

Add in a script that checks for when your game has received focus again, then explicitly start playing the sound again.

void OnApplicationFocus() {
        audio.Play();   // Put your code here to start your background music...