title: Why my WPF application has Drag & Drop disabled (even when AllowDrop is true)?
body: <p>My WPF application inhibits the Drop of files from Windows Explorer, showing a Stop-sign cursor.</p>
  
  <p>I've tried setting the AllowDrop property (that of the UIElement ancestor) to true on the main window and contained controls, but no luck at all, no drag-drop events are fired.</p>
  
  <p>Any ideas or suggestions to find the cause?</p>