Nano iPod will not charge in audio system

I bought a Element iPod Hi-Fi Audio system EIPS100 ar Circuit City before they went out of business. It works find, except when I put theiPod nano in the slot on top of the system, I geta message that says "Charger is not supportedwith this accessory". The info that comes with the system says it provides synchonization,recharging and playback for your iPod. Do youhave any idea what would cause this ?ThanksDenny