i was just making my first steps in swt world and i faced that strange exception

Java Code:
** (SWT:7229): CRITICAL **: giop_thread_request_push: assertion `tdata != N
this message appears in console after i close the application...
the swt code it self is very simple and i dont know if it was the reason for that exception...any way here it is
Java Code:
		Display display = new Display();
		Shell shell = new Shell(display);
		shell.setText("Hello world!");
		GridLayout gl=new GridLayout();
		gl.numColumns=2;
		shell.setLayout(gl);
		Combo combo = new Combo(shell, SWT.READ_ONLY);
		combo.setItems(new String[] { "A", "B", "C" });
		combo.setSize(100, 200);
		
		Label label =new Label(shell,SWT.CENTER);
		label.setText("ahmed");

		Label label2 =new Label(shell,SWT.CENTER);
		label2.setText("kotb");
		
		shell.pack();
		shell.setLocation(display.getPrimaryMonitor().getBounds().width/2, display.getPrimaryMonitor().getBounds().height/2);
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch())
				display.sleep();
		}
		display.dispose();
thanks in advance...