I have the same issue today. Regard to instructionA5E00124881-05 "ET 200S Serial interface modules" code from picture is 0836 hex and as you probably already know it means:

However, I get more error codes during the polling e.g. 0810, 0811 but all parameter for both sides of connection are the same (modbus type, boundrate, stop bits, parity, control flow = no control etc.). Physiacal connection also positive (I've changed cable for different one - no help, the same reactions on polling) - no wire brakes on both cabels.

I've even try to change "magic variable" called >>>Expiration Character Time Multiplier <<< without succeed.

Maybe we do something wrong "in newer ending loop" ?

Any ideas ?