I have recently replaced a defective 2412N SmartLinc. I have been able to link only 2 out of 14 Insteon devices. The SmartLinc does not recognize the remaining 12 devices. I have 2 Wireless Phase Couplers 2443 installed on opposite phases within the house.
When I originally installed the SmartLinc (2010), I was able to connect most of the devices (all but one).
This sounds like the SmartLinc might be attached to something that is absorbing most of the energy from passing signals. Is there a ups or some kind of noise/surge filter plugged in nearby? Did you move or add a cell phone or laptop computer charger to the same area?