Mhmm, besides an obvious typo ('0 or .F.' before isotrack) I can think only of one problem: .null., i.e. where you'd pass Nothing in VB.

One of my internal apps controls a banking client program via COM and there I had the same problem - I needed to pass .null. to a method but Fox would not let me. Fortunately I could work around this by creating an empty object of the correct type and the called method did the same as it would have done if I had passed .null.

Unless our resident wizards come up with a solution I think this should go on the VFP bug list, because it is a showstopper if your app needs the COM control in question and you cannot convert the app to Delphi or some other language ...