Unable to shut down my iMac

Just bought the UR22mkIl, installed it with latest update 9.5.21, connected to my iMac, running Sierra 10.12.6. Unable to shut down the iMac with the UR22mkII connected - instead the computer shows an error, then starts back up again. WTF?

Are you using the latest Yamaha Steinberg USB Driver?

Thanks - the latest driver worked (at least for now).