Turn off your FaderPort 8.
Open the Audio MIDI Setup application. Finder > Applications > Utilities > Audio MIDI Setup.
Once you've opened the Audio MIDI Setup application go to Window > Show MIDI Studio.
Remove all FaderPort and FaderPort 8 devices from the MIDI Studio.
Power on the FaderPort 8 and try updating the firmware again from Universal Control.
If you need further assistance please submit a technical support request at support.presonus.com