Native OS X doesn’t allow nested modal dialogs. There is nothing Panorama can do about that. (I believe nesting did work in Panorama 6, because that was using Carbon instead of Cocoa.)
If you can switch to a sheet instead of a standalone modal dialog, nesting does work. In most cases, sheets are more “OS X” like anyway. All you have to do is add the line
sheet=true
to the dialog options.