Go to Device Manager, Hardware, be sure the CF card is not trying to be installed in Comm 1 or Comm 3 as those ports are normally taken by other built-in devices and cause conflicts. You will most likely see an exclamation sign next to the port in use. You need to resolve the conflict such that the comm port that is assigned by Windows to the SuperNAV GPS CF card appears without an exclamation sign. Please also see instructions.