o  already exists

    A csma-cd station entity by that instance name already exists.

 o  contraint violation

    That controller is already in use by some other csma-cd station.

 o  process failure

    The communication port provided is invalid.

 o  communication port in use

    The communication port is already reserved by another entity.

 o  invalid communications port

    You cannot run CSMA/CD data links on this communications port.

 o  no such object instance

    The CSMA-CD module has probably not been created yet.   On
    OpenVMS, verify the contents of your NET$CSMACD_STARTUP.NCL
    script.  You may need to run net$configure to reconfigure your
    devices.