We've got a system with numerous XL50s, XL10s, an XL500 all over LON coming back to an iLON and going to a SymmetrE system. About every other month the XL50s will drop off the SymmetrE system and they are no longer visible, but everything else still is. After looking at the system with Excelon you can see that the program IDs have all been blown away and restored to their default of ending in FF, where the cbus address usually is. The 50s can still be communicated with remotely through the 500 controller. The system can be returned to a functioning state with a redownload to each XL50 and a resynchronization. Echelon has said something to the effect that the program ID is written to the neuron chip on a controller reboot. My question is what could cause the program ID to get blown away and what can you do about it or what things should be looked at?