Am I missing something? I use the "Delete Modem (PLM)" option in the admin console. It provides no feedback or errors. The next time I reboot ISY with the PLM physically disconnected, ISY boots into safe mode because it can't communicate with the PLM.
The last Insteon device I had connected was removed over a year ago so there are no more Insteon devices configured with the PLM.
ISY v 5.3.4