No type was found that matches the controller named 'User'

I'm trying to navigate to a page which its URL is in the following format: localhost:xxxxx/User/{id}/VerifyEmail?secretKey=xxxxxxxxxxxxxxx

I've added a new route in the RouteConfig.cs file and so my RouteConfig.cs looks like this:

public class RouteConfig
{
    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "VerifyEmail",
            url: "User/{id}/VerifyEmail",
            defaults: new { controller = "User", action = "VerifyEmail" }
        );

        routes.MapRoute(
            name: "Default",
            url: "{controller}/{action}/{id}",
            defaults: new { controller = "Home", action = "Index",
                id = UrlParameter.Optional }
        );
    }
}

Unfortunately, when trying to navigate to that URL I get this page:

<Error>
    <Message>
        No HTTP resource was found that matches the request URI 'http://localhost:52684/User/f2acc4d0-2e03-4d72-99b6-9b9b85bd661a/VerifyEmail?secretKey=e9bf3924-681c-4afc-a8b0-3fd58eba93fe'.
    </Message>
    <MessageDetail>
        No type was found that matches the controller named 'User'.
    </MessageDetail>
</Error>

and here is my UserController:

public class UserController : Controller
{

    // GET      /User/{id}/VerifyEmail
    [HttpGet]
    public ActionResult VerifyEmail(string id, string secretKey)
    {
        try
        {
            User user = UsersBL.Instance.Verify(id, secretKey);
            //logger.Debug(String.Format("User %s just signed-in in by email.",
                user.DebugDescription()));
        }
        catch (Exception e)
        {
            throw new Exception("Failed", e);
        }
        return View();
    }
}

Please tell me what am I doing wrong?

In my case after spending almost 30 minutes trying to fix the problem, I found what was causing it:

My route defined in WebApiConfig.cs was like this:

config.Routes.MapHttpRoute(
    name: "ControllersApi",
    routeTemplate: "{controller}/{action}"
);

and it should be like this:

config.Routes.MapHttpRoute(
    name: "ControllersApi",
     routeTemplate: "api/{controller}/{action}/{id}",
        defaults: new { id = RouteParameter.Optional }
);

as you see it was interfering with the standard route defined in RouteConfig.cs.