I occasionally get the message 'Device not available' for the Radio or the Media Inputs in my GLC. HTe only way to get the entertainment working is to stop the car. Get out. Lock it. Leave it for 10-15mins. Then get back in and all works fine. Any suggestions on how to prevent this problem or reset it on the move? It has been back to the dealer who did a software update, but still the problem occurs intermittently.