How to set Session Timeout in ASP.Net MVC

session time out perfectly working if i running form my machine  but if i hosted its not working perfectly its redirecting to error page called "server error   /   in application" ?

how to solve this in mvc ? in mvc do i need to use diffrent code ? 

My code in web.config

<authentication mode="Forms">
      <forms loginUrl="~/Home/Home" slidingExpiration="true" timeout="20"></forms>
    </authentication>