You have a corrupt or outdated JetAdmin port monitor.

Download the latest version of JetAdmin

                 or

. Create a LPR port for each JetDirect card.

. Using the printer Properties on each printer, move it to it's LPR port.

. Uninstall JetAdmin.

. Shutdown and restart the print server.

. Use Control Panel / Services to Stop the Spooler.

. Use Regedt32 to navigate to
  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Print\Monitors
  and remove the JetAdmin Port Monitor.

. Shutdown and restart the print server.