DragAndDrop class

Hi,

I'm trying to use this code from the DragAndDrop documentation, but it's giving me an "Invalid Cast Exception" error for the DragAndDrop.objectReferences line...

I don't understand what kind of object it needs...

Thanks in advance!

function restoreSelection(o : Object){

     // Clear out drag data
     DragAndDrop.PrepareStartDrag ();

     // Set up what we want to drag
     DragAndDrop.objectReferences = o;

     // Start the actual drag
     DragAndDrop.StartDrag ("bookmark");
 }