Your route seems to be messed up. Try the code below to configure your routing.
public override void RegisterArea(AreaRegistrationContext context)
{
context.MapRoute(
"Admin_default",
"Admin/{controller}/{action}/{id}",
new { area="Admin", action = "Index", id = UrlParameter.Optional }
);
}
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new {controller = "Startup", action = "Index", id = UrlParameter.Optional }
);
}