Multi select don't work in my script

Hi this is a scriptlet, from A script I am making. It is a listbox I am filling with selected nodes of the scene. It needs to be multi select, but I cant multi select in the listbox. I try to use extended here, but I also try to use Multi. Both are not working. What is the problem?

/*********************************************************************/
// Globals
/*********************************************************************/
var selNodes = Scene.getSelectedNodeList()		// Get the selected nodes from te scene
var nSelNodes = selNodes.length;				// The length of the selected node array


// Create and define DzListBox: 'Surfaces'
var Surfaces = new DzListBox( Dropper );
Surfaces.setGeometry( 190, 21, 171, 181 );
Surfaces.SelectionMode = Surfaces.Extended;
for( var i = 0; i < nSelNodes; i++ )
{
	if( selNodes[i].name != selNodes[i].getLabel() )
	{
		Objects.insertItem( selNodes[i].name + "/" + selNodes[i].getLabel() );
	}
	else
	{
		Objects.insertItem( selNodes[i].name );
	}
}