I opened the unit up looking for a hardware problem and I found one. The connector from the PSU board to the top relay board (relays 1-4) was mis-pinned so that only one of the 2 pins was plugged in. I bought the unit used. In fact I bought 2 of them and the PSU & GC from a local guy. I gotta assume a previous owner had been inside of the unit. I can't imagine this would have gotten past QC at the MFR.
Q & A for building and interfacing your rack gear with Ground Control Pro and GCX-based systems.