ASP.NET MVC Routing "The resource cannot be found"

I have a controller which inherits from a base controller and the default routing:

 routes.MapRoute(
                "Default", // Route name
                "{controller}/{action}/{id}", // URL with parameters
                new { controller = "Home", action = "Index", id = UrlParameter.Optional } // Parameter defaults
            );

works correctly when going to /Departments/Create:

public class DepartmentsController : BaseController
{

    public ActionResult Create()
    {
        return View("Create");
    }

public abstract class BaseController : Controller
{
....

However if I try and change this to be a generic controller e.g.

public class DepartmentsController<T> : BaseController<T>
    where T: class
{

    public ActionResult Create()
    {
        return View("Create");
    }

public abstract class BaseController<T> : Controller
    where T: class
{
....

Then going to /Departments/Create I end up with a "The resource cannot be found" error suggesting that the action has not been found. However, when I check the routes used with routeDebugger I can see that "{controller}/{action}/{id}" has been matched yet the action has not been called:

Is there a different route or method I would have to use to be able to call the correct action?

Thanks!