Errorhandling after HttpSession time-out / JspWithNoErrorPageException

  I want to send 'errorpage.jsp' when an Http-session time-out occurs. I
  tried to capture this in my controlling-servlet but when time-out occurs,
  a standard error-text is shown with errorcode 500 etc...

  Why is my errorpage.jsp not comming up properly? The stderr.logfile shows
  the additional info I send, so I'm sure it's executed. The path is also
  correct.

  1) Here is how i do this
  if (session.isNew())
  {
  System.out.println("Previous session was Time-out");
  System.out.println(" Desplay errorscreen ");
  httppage = "/jsp/errorpage.jsp";
  getServletConfig().getServletContext
  ().getRequestDispatcher(httppage).forward(req, res);
  return;
  }
  ...
  rest of processing

  2) This is a piece of the error i receive in webserver:
  com.sun.jsp.JspWithNoErrorPageException: Server caught unhandled
  exception from JSP ?errorpage.jsp!

  3) This is a piece of the errorpage I receive in the browser:
  Error 500
  An error has occured while processing request:
  http://www.clippersupport.be:2031/servlet/com.clipper.servlets.FQControll
  er
  Message: Server caught unhandled exception from servlet [invoker]: Server
  caught unhandled exception from servlet
  [com.clipper.servlets.FQController]: Server caught unhandled exception
  from servlet [jsp10]: Server caught unhandled exception from JSP
  [errorpage.jsp]

  Target Servlet: invoker
  StackTrace:
  -------------------------------------------------------------------------
  -------
  Root Error-1: null

  java.lang.NullPointerException
  ...
  rest of page