Unable to populate a StateDiagram using automation interface

I'm trying to populate a StateDiagram with only a subset of State items contained in the StateMachine (State having a specific stereotype), but I'm unable to create new Symbol for each State to add in the state diagram.

The following returns this error "Unable to create an object across this role (Class=2095, Role=8270)":

    Set NewSymbol = MyState.Add("SD State")

Any idea on the way to create a new symbol for a State Item ?