Not sure what you're talking about. Did you use -4 as the 3rd parameter in $dialog()? The only condition is that the parent dialog must be active for that to work, but in the vast majority of cases you only want to open a modal dialog from an event coming from the parent one (e.g. user clicking a button). Otherwise you could activate the parent dialog (with /dialog -ev dname1) before calling $dialog(dname2,table2,-4).
