session lost problem

[kundan varma]

Hi all
I am working on a project where we are storing session in stateful session bean.When the session gets lost depending on the session-timeout property of orion-ejb-jar,i want to open the login page again.Our architecture is much like struts using session bean from action classes.EJB's are deployed on oc4j release 3 presently.When i am trying to redirect the page using request dispatcher, it is giving null pointer exception.I am getting the request dispatcher object but cant invoke any of its method.
PLz help
thanks
candy