Modbus RTU Exception Code -203

I cannot find this exception code -203 anywhere in Pac Control Modbus kit or in the Modbus specification, or online for that matter.

The code is showing up in function 16 write floats.
Does anyone know what code -203 means?

Its in the list: Driver could not be found or loaded.

I saw that, but did not quite make sense. I assume the list is based on Opto22 codes and not Modbus. I would assume that the code is actually coming from the Krohne flow meter, but this is not a Modbus exception that exists in the specification. I suspect that Krohne made it up for their own purposes. This came from “n16AsFloatStatus”, so not sure if it is a legit code. I put the question to Krohne guy via email, probably know smething tomorrow, unless you can expand on this.

It is a result of a comm handle not opening, in this case, overlooked changing the com handle to the correct one and it tried to load the default one which was not configured…
It should read, “comm handle not configured or session limit reached”.
Also, I was confused because this seems more like a “n16AsFloatSubStatus” versus a Modbus exception code.

Looks like an Opto22 error code to me. The integration kit sample strategy returns some pre-defined error codes (none of which are -203), the modbus error codes (which are not negative) or whatever error code OpenOutgoingCommunication or TransmitString returns to that status variable.

My guess it is a problem with the comm handle and OpenOutgoingCommunication is throwing the error.

I traced it down, it is coming directly from the OpenOutgoingCommunication return value.
But since it was showing up in the n16AsFloatStatus, I was assuming it was from the Krohne.
It is right where they try to open the handle. I guess they had to use the n16AsFloatStatus because there was no way to pass it to the n16AsFloatSubStatus?