Cause
This error occurs if your application code assigns a value to a constant reference. The constant reference can include the following.
Global, class, or local constants.
Method parameters defined as constant or input.
Method parameters are constant by default, so parameters cannot be assigned to unless they are explicitly defined as being io or output.
The self variable.
You cannot assign to self, except in a primitive method.
This error is also returned if your code assigns to an expression that ends in a type cast. You cannot assign to type cast expressions.
Action
Remove or correct the invalid assignment. If you are assigning to a parameter and you intend to export the value of that parameter to the calling method, you should define the parameter as being io or output.