draggingUpdated: event is not called on overlay window.

Hello,
Having problem when i drag and drop an image/folder from iphoto right panel and finder over the overlay window which is kept over my applications dock icon.I also have added the pasteboardtype NSFilesPromisePboardType which i think is the type for iphoto right panel and finder.The problem is i am not getting draggingUpdated: event while if i drag from the left panel of iphoto i get this event.
i need the help in urgent i am tryiong a lot but no success so far.
What i am doing is i want to put different images over the overlay window depending on the mouse position but as i am not getting any draagingUpdated event i am failed to do that.
thanks in advance..
Sudeep Dua