Aprilaire system goes bonkers

[asteinmetz]

I have 5 8870 Tstats wired into an 8818 distribution panel and thence to a an 8811 protocol adapter and finally to Homeseer.  Power to the stats comes from the panel.  This system has been working fine for 4 years (thanks to this community back when I was setting it up) but now the stats all go crazy when the 8811 is plugged in.  Temperature readings are crazy.  Humidistat functions appear and the stats all read zero degrees to homeseer.  On the distribution panel the "B" light (transmit) glows steadily if the protocol adapter is unplugged and the "A" light (receive) glows steady if the adapter is plugged into the distribtution panel.  The behavior doesn't change if homeseer PC is or is not connected to the protocol adapter.  When the 8811 is disconnected the stats all work normally.
 
I thought the 8811 might have gotten fried but when I swapped in a new one, nothing changed.
 
Any clues? Thanks.

 

[hedg12]

I know that power issues can create major weirdness with 8870s - you might verify the power supply for the panel. Other than that, has anything changed in the system?