This error is often related to USB timing. Try using different USB ports, or other Dock Connector to USB Cable. Refer also to the other USB troubleshooting procedures available, proposed in Article iOS: Troubleshooting USB connection. If you use a docking station, connect the device rather directly to the USB cable for Apple Dock connector. If the problem persists on a reliable computer, you may need to repair. If a USB troubleshooting insulation has not solved the problem and you do not have any other computer, follow these steps:
- Connect the device to iTunes and verify that the device is in recovery mode. If this is not the case, place it in recovery mode;
- Perform Restore and wait for error.
- When prompted, click OK.
- Close and reopen iTunes while leaving the connected device.
- The unit should again be recognized in recovery mode.
- Proceed again to restore.
If the above steps do not resolve the problem, try to restore using a USB cable, a computer and a reliable network connection