When “CHECK DEVICE” is displayed

This message is displayed under the following conditions.

When there is a short in the USB bus When an unsupported device (for example a USB mouse) is connected When an unsupported iPod® is connected When a connected iPod® is frozen When a transmission malfunction occurs When an iPod® confirmation malfunction occurs
When a HUB class USB storage device is connected

Disconnect the USB storage device/iPod® and check it.