Need a help on Session_OnEnd()

Question

Hi Guru's I need a help on this actually i have following stuff:

1) I need to show error page to user once session is end ( by default is 20 min)
2) I am using windows Authentication
3) All my pages( Except error page) inherited form base page Where am taking care of all authentication related Stuff before actual page render.
 
Now take following in consideration
1  user time out elapsed.
2. gobal.asax --> Session_OnEnd() event fires in this event i need to write code to rediect user to error page with appopriate message.

As i tried Respose.Redirect & server.Transfer these objects not woking. Any idea for this.

Thanks in advance.