get the Tapedrive checked, often this is and Hardware error.
To reset the incorrect Media status use the command Bob provided, but take the time to verify the Media on another Drive sometime soon as well, just to be sure.
If you get the Error on a different Drive as well it could also be the connection to the MediaServer or some Program on the Server itself. Especially Monitoring-Software that also does SAN-Scans can be nasty here.
