Wonderware to Yaskawa PLC (Modbus)

I'm creating a new HMI to communicate with a Yaskawa controller. I started adding some of the values to the screen from the 4XXXXX registers and they look fine. I also added a discrete button writing to 000013 and the log viewer is giving me some errors about function code. I would assume Wonderware is using FC5 as I am sure the previous HMI (Uticor) was doing the same thing.
There are not many options I can change in the driver (DASMBTCP 3.0).
Any ideas?

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwjP7MTasYrRAhWZ3oMKHf0JCz8QFgg2MAE&url=https%3A%2F%2Finsource.mindtouch.us%2F%40api%2Fdeki%2Ffiles%2F1260%2F%3DDASMBTCP_3.0.pdf%3Frevision%3D2&usg=AFQjCNGoToJjF2fD14Yd6RyRKiDF9rMoTg

"The function code received in the query is notan allowable action for the slave. This may be because the function code is only applicable to newer controllers, and was not implemented in the unit selected. It could also indicate that the slave is in the wrong state to process a request of this type; for example, because it is unconfigured and is being asked to return register values."

What is the controller model that you are communicating with?

Could it be a "one offset" address issue with the coil number?

Note the statement (from the Modbus spec) that "coils are addressed starting at zero. Therefor coil numbered 1 is addressed as 0."

In the example, the target address is Coil 173 (decimal)
173 decimal is (00)AD hex, but address used is (highlighted) 00AC hex (172 decimal) since the count starts at zero.

Not all bits are always read/write. some can be read only. If you're writing to a read-only bit, then the slave cannot execute.