Probléme drag and drop en jtree

Qui a trouvé ce type de exception dans un projet de drag and drop JTREE:
Exception in thread "AWT-EventQueue-0" java.awt.dnd.InvalidDnDOperationException: Drag and drop in progress
at sun.awt.dnd.SunDragSourceContextPeer.setDragDropInProgress(Unknown Source)
at java.awt.dnd.DragSource.startDrag(Unknown Source)
at java.awt.dnd.DragSource.startDrag(Unknown Source)
at com.telnet.projet.DndTree.dragGestureRecognized(DnDTree.java:52)
at java.awt.dnd.DragGestureRecognizer.fireDragGestureRecognized(Unknown Source)
at sun.awt.windows.WMouseDragGestureRecognizer.mouseDragged(Unknown Source)
at java.awt.AWTEventMulticaster.mouseDragged(Unknown Source)
at java.awt.Component.processMouseMotionEvent(Unknown Source)
at javax.swing.JComponent.processMouseMotionEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)