Emerson Exchange 365

I want to switch between RCAS and CAS using some logic based on operator selection of natural gas or methane.

I am using MODE parameters to do this, but there seems to be something I am missing to make this work.

When the operator switches mode there is a integrity error in the CALC block with it trying to write to the PID1. I can clear the problem by moving the NORMAL MODE from the mode I want to MANUAL. The PID gets written to, the faceplate changes, I am permitted to choose the mode I want.

 So what am I missing that is preventing a nice smooth transition between the modes?

thanks

Gary