Here's an important safety tip - when you're creating a class-based control module and you include a function block that uses structured text (CALC, CND, ACTION) and you check the box labeled "Allow instance expression to be configured", all parameter references have to be external.
For example, if you've got a CALC and you'd like to tie the OUT1 to IN1 for an instance of a module class:
You'll get this error message when you try and save your expression:
