DR series inverter stacking problem

I think I've solved the problem. 

Xantrex supplies a stacking cable with only 4 wires.  It's has a telco style modular connector at each end.  I replaced it with a similar cable but with 6 wires.  The extra two wires connect to the outer two contacts in the connectors on the inverters.  Both outer contacts are grounds and they add shielding to the communications signals between the two inverters.  Without those two extra wires, the inverters would lose communication with each other and shut down. 

I discussed the different cable with the Xantrex support tech.  He said there'd be no problem using the 6 wire cable instead of the 4 wire. 

The system ran for over three weeks and was still working when we had a power outage yesterday.  It supplied power when I needed it and charged the batteries when the power came back on. 

Thanks to all who offered suggestions.