Serato DJ Lite or your operating system may not recognize the unit as a controller.

Mac

Follow the instructions in the troubleshooting guide [here].

http://faq.pioneerdj.com/files/img/Troubleshooting_macOS_001_E.pdf

Windows

Refer to Case 3 in the guide [here].

https://www.pioneerdj.com/-/media/pioneerdj/downloads/other/troubleshooting/troubleshooting_002_e_v011.pdf

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.