External file drag and drop into gadget using Silverlight 4.0 - not working.

XAML Code:
<StackPanel Background="DarkGray" AllowDrop="True" Drop="StackPanel_Drop">

private void StackPanel_Drop(object sender, DragEventArgs e)

1. Function -> not calling:--> what is the issue?
2. Gadget External file drag and drop - not support?
3. How to fix?

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