I have a list box with five values A, B, C, D, E. I need a condition that a user can select B and C together if they want but never with any other field. the other field can only be selected as alone meaning D, E, A can only be selected alone and B can only be selected with C only not D nor E no A
I'm not sure if I would want to solve such dependencies with a listbox which would probably require the use of listbox-expressions and/or actions which check the selection and remove then again if they are not valid like defined. I would think on applying calculation-conditions within the objects and adding a short customized error-message to them to inform the user why the calculation didn't happen.
I agree with marcus_sommer. If you feel you must do this at all try two listbox objects. One with the expression if(Match(MyField, 'A','D','E'),MyField) and the other if(Match(MyField, 'B','C'),MyField). Then use the conditional display option on the Layout tab to hide the listbox if a selection is made in the other one. You can use conditions like =NOT max(match(MyField, 'B','C')) and=NOT max(match(MyField, 'A','D','E'))