Question

I am trying to use it for Login page.

if (Session["UserID"] == null)
     Server.Transfer("/Account/Login", true);

But I get The Exception -> Error executing child request /Account/Login.

Answer 1

To use a server transfer method you could look at this from Simon Weaver, but in the context of your question I would use a redirect action instead.

RedirectToAction(new {
   controller="Account", 
   action="Login"
});

to get it to tell the login controller where to go back to try

RedirectToAction( new {
   controller="Account",
   action="Login",
   new RouteValueDictionary { 
      {"actionToGoBackTo", "theActionName"},
      {"controllerToGoBackTo", "theControllerName"}
   }); 

note that the Login action will need to take two string arguments, actionToGoBackTo, and controllerToGoBackTo.