Usually, you use the detail0 turret subobject not the detail1 subobject. Not sure if that alone could break it. They're also set to no movement. Is the ball supposed to move and shoot or remain stationary? I'm also not sure what the purpose of the turretholder object is. It's not visible as far as I can tell, nor part of the turret. Why not just make it part of the main mesh? Seems a waste of a subobject to me.