xbox 360 drums stop after 15 seconds in garageband

I'm using an xbox 360 drum kit with garageband (via miditar hero as the midi controller) just as a starter for my 10 yo son to see if he will get into drumming. The drums play fine through garageband but stop after 15 seconds. when I change software drum kits the sound starts again for 15 seconds and then stop again. I can play the drums just through miditar hero and it doesn't stop but then can only have the default grand piano sound. Anyone have any ideas?

Thanks

Jim