ASP.NET Back Button Issue

Hi,

I have an issue with the back button on a web form which enables the user to go back to the previous page. My application functions so that when an unexpected error occurs, I display an error page. At this point I do not want the user's to be able to hit the Back button to go to the previous page. I want them to close down the site and start over. How do I set up my application to not let the user go back to previous page when an error occurs? I would even like to be able to display the "Expired Page Error" page when they press the back button. Anywhich way I would be happy. I have seen a bunch of posts on Google Groups and other sites and I was never able to get anything to work.

I would greatly apreciate the help....

Thanks