This issue is related to the client device that is trying to join a host, when its video decoder is not working correctly. Potential reasons for this are further below.

Your device is pending a restart due to a driver update

If you manually updated or your system automatically updated the graphics drivers, you need to restart the machine and try to use Parsec again.

Parsec disabled the decoders because of a crash

In your Parsec settings, you may see the message 'Some decoders have been disabled by a previous crash when querying decoders.' and a button to 'Re-Enable and restart'. This means that your GPU decoder caused Parsec to crash previously, and it was disabled to allow Parsec to start, but as a result, it is not used in the app.

You can try to use the button to re-enable, and it may resolve the issue. It may alternatively crash the app again and cause the message to reappear, in which case, you may need to try cleaning up and reinstalling your graphics drivers, or try to select a different Decoder in your Parsec settings.

Your drivers are faulty and need to be reinstalled

If you haven't already done so, consider cleaning up and reinstalling your graphics drivers.