OK, thanks for that info.
I have plugged in the PLM and the ISY in that order and am still having a problem. If I go to 'Show PLM Links Table' and click on Count the number shown is '0'.
When I attempt to 'Restore Modem (PLM)' the dialog box comes up and closes within two seconds. I attempted to reset the PLM by holding down the set key for 10 seconds and it did not help.
What else can I try?