Aurender W20 clock invalid??

Are you using an external clock?  If not, there could be a menu setting for internal or external clock.  If it's set to external and you aren't using an external clock, you would get an error. 

I don't have an Aurender, but that's how my dac works. 

No external clock

you might check your menu settings. Below comes from your owner's manual.

9. Coaxial BNC Word Clock Input

Connects to the BNC output of the master/word clock. Use a 75 ohm coaxial cable. Configure word clock input preferences in the "Advanced 2" section of the Settings menu.

I do not own an AURENDER W20 but found the info below:

“The “CLOCK IN: INVALID” message on the Aurender W20 indicates a synchronization issue with the clock signal. This problem can cause the music to drop or cut out intermittently. To resolve this, ensure that all connections are secure and that the clock settings are correctly configured. If the issue persists, contacting Aurender support for further assistance may be necessary”.

“There are specific settings in the Aurender W20 that need adjustment for clock synchronization:

1. Clock Synch Setting: In the W20 settings menu, you must enable the Clock Synch feature to ensure proper synchronization with external clocks.

2. RS232 Control: Use the RS232 control to toggle the clock frequency settings to match the data rates, such as 44.1kHz or 48kHz, to prevent synchronization issues.

3. Conductor App Settings: Verify and adjust settings in the Aurender Conductor app, as certain configurations might be necessary depending on the version of the app”.