I tried increasing the timeouts and got some moderate improvements, but still saw these timeout errors. This was over Ethernet.
When I connect to the USB port on the PLC and use bridge mode I can program all the EX-RC1s.
The CANBUS cable is Belden 3084, which I believe is what Unitronics specified or used as an example in their data sheet. All devices are daisy-chained, with 120 ohm resistors at each end. Baud rate is 500K.
I'm wondering if the ethernet switch I'm connecting through may be contributing to the problem.
Mark