Intermittent Ipod failure

[bher]

Does someone could explain why my E92 M3 recognizes my ipod sometimes yes and sometimes no?
Most of the times, it is working but sometimes starting the car a second time, the ipod (connected tru the double cable) is not red AND while starting the car a few hours later for third time that day e.g. it is playing the following of the song from the first ride.
Thanks