There's a couple of ways to investigate, in easy to try order:
It's rare, but I have been shipped devices that need to be factory reset to get working
How old is your PLM, 5+ years? The "lost connection" to a couple of switches comment makes it suspect. Unplug it wait 10 seconds, and plug back in. If this fixes the problem, its not a fix, you are on borrowed time and need to replace it.
Is the switch far away in your home, far away from the PLM and other Insteon wireless devices? It's a pain, but temporarily wire it in closer to your PLM. I have a 3 prong plug-in cord end from the hardware store I use for setting up and testng... see if it works nearby the PLM