Try these solutions:
1. Ensure that all the steps within the USB Audio section of the manual have been followed
2. Not all Windows versions support playback at sample rates greater than 384kHz
If you experience issues please set the default Windows playback format to 384kHz or lower, then restart your Network Player.
More information can be found by following the PC Setup steps in the manual here.
3. Ensure that the USB Audio source has been selected via the app or the front panel source selector
4. If you are connecting a Windows PC, make sure that the correct USB driver is downloaded
The driver is available here.
5. Ensure that your PC/Mac is connected to the USB Audio input with a USB A to B cable