rekordbox or your operating system may not recognize the unit as a controller.
Follow the instructions in the troubleshooting guide [here].
Refer to case 5 in the guide [here].
You may solve the issue by doing the following:
- Disconnect any USB hubs and connect the unit directly to your PC/Mac.
- Disconnect any other USB devices.
- Quit all other applications.
- Connect to a different USB port.