when i click back or forward button wont display direcly on pages .it ll ask login page .after i logout

for this u have to stop browser from caching a page use this following code on page load event for this u dont want cache by browser.
Response.Cache.SetCacheability(HttpCacheability.NoCache);
If you want to apply that for all of your pages, you can place that code in the Master page Page_Load event.