How could i disable that the users won't be taken back if they click
back button but only Page Expired Page will be displayed.

The user will always be taken back if you click the back button - you have
no control, over the browser buttons only how the page is interacted with.

You can however set the
Response.Cache.SetCacheability(HttpCacheability.Public option. I cant
remember the exact settings for this so you'll need to look at it closer.
You can also try working with the javascript history object ie: <script
language="javascript"> window.history.go(1).

--
Regards

John Timney (Microsoft ASP.NET MVP)
----------------------------------------------
<shameless_author_plug>
Professional .NET for Java Developers with C#
ISBN:1-861007-91-4
Professional Windows Forms
ISBN: 1861005547
Professional JSP 2nd Edition
ISBN: 1861004958
Professional JSP
ISBN: 1861003625
Beginning JSP Web Development
ISBN: 1861002092
</shameless_author_plug>
----------------------------------------------

[quoted text, click to view]