I think that if you want to add new elements to a set that corresponds to one of the indices of an argument parameter, you will also have to provide the correspoding set as an explicit In/Out argument such that you can add new elements to that set
LS_available_sections is not argument parameter but it is argument set.
After changing property of argument set from output to INout also, I am facing same error
Based on just the text you provided for me it is quite difficult to see what is going on.
Can you select all of the identifiers that are related to the above (i.e. the procedure, the sets) in the model tree, then right-click on it and click on “Text Representation” for the selected parts and post that here.
Unless somebody of AIMMS has a direct idea what this could be?
I solved this problem. Thanks for your time.