🚀 go-pugleaf

Hello all,
Here is my problem. I have a class with decleration...

public class EfzinCalendarManagerFrame extends EfzinInternalFrame

The super class has the following code..

public class EfzinInternalFrame extends JInternalFrame
{
   //Data
members-------------------------------------------------------------
   private static int openFrameCount = 0;
   private static final int xOffset = 30, yOffset = 30;
   private static Vector addedFrames = new Vector();
   private static boolean selectedStatus = false;
   private static Object selectedFrame=null;

//Methods------------------------------------------------------------------
   public EfzinInternalFrame()
   {
      super();
      addedFrames.add(this);
      openFrameCount++;
      try
      {
         jbInit();
      }
      catch (Exception e)
      {
         e.printStackTrace();
      }

   }

   private void jbInit() throws Exception
   {
      //Set Default close operation
      setDefaultCloseOperation(HIDE_ON_CLOSE);
      this.addInternalFrameListener(new InternalFrameAdapter()
      {
         public void internalFrameDeactivated(InternalFrameEvent e)
         {
            EfzinInternalFrame.deActivateGetSelectedFrameMethod();
         }

         public void internalFrameActivated(InternalFrameEvent e)
         {
            EfzinInternalFrame.setSelectedFrame(EfzinInternalFrame.this);
         }

      }
      );

   }

When i turn the EfzinCalendarManagerFrame  to the designer a i get the
ordinary message...

Failed to create live instance for variable 'this'. null
class java.lang.NullPointerException null

The problem is that EfzinCalendarManagerFrame   extends EfzinInternalFrame.
If i change the extends statement from EfzinInternalFrame to JInternalFrame
i will not get error. The weird is that when i open the EfzinInternalFrame's
designer tab all are correctly. Do you know a possible reason of this
annoying behaviour?(I dont implement any abstract class either an interface)
Thank you for advance.