I assume it's connected via the USB connector kit? Not had any problem, it's not an IOS7 problem is it?
Got a dedicated iPod plugged in to the connector kit and works ok.
I get 'unsupported' displayed from time to time (really annoying) quick soft reset of the iPod fixes it. Try soft reset on the iPhone. Both home and power button pushed in for 5 secs until the apple logo appears.