public class MefControllerFactory : IControllerFactory
	{
		private string pluginPath;
		private DirectoryCatalog catalog;
		private CompositionContainer container;
		private DefaultControllerFactory defaultControllerFactory;
		public MefControllerFactory(string pluginPath)
		{
			this.pluginPath = pluginPath;
			this.catalog = new DirectoryCatalog(pluginPath);
			this.container = new CompositionContainer(catalog);
			this.defaultControllerFactory = new DefaultControllerFactory();
		}
		public System.Web.SessionState.SessionStateBehavior GetControllerSessionBehavior(System.Web.Routing.RequestContext requestContext, string controllerName)
		{
			return SessionStateBehavior.Default;
		}
		public IController CreateController(System.Web.Routing.RequestContext requestContext, string controllerName)
		{
			IController controller = null;
			if (controllerName != null)
			{
				Lazy<IController> export = this.container.GetExports<IController, IDictionary<string, object>>().Where(c => c.Metadata.ContainsKey("ControllerName")&& c.Metadata["ControllerName"].ToString().ToLowerInvariant().Equals(controllerName.ToLowerInvariant())).FirstOrDefault();
				if (export != null)
				{
					controller = export.Value;
				}
			}
			if (controller == null)
			{
				return this.defaultControllerFactory.CreateController(requestContext, controllerName);
			}
			return controller;
		}
		public void ReleaseController(IController controller)
		{
			IDisposable disposable = controller as IDisposable;
			if (disposable != null)
			{
				disposable.Dispose();
			}
		}
	}

ControllerBuilder.Current.SetControllerFactory(new MefControllerFactory(
                    Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Plugins")));

[Export(typeof(IController))]
[ExportMetadata("controllerName", "Demo")]
[PartCreationPolicy(CreationPolicy.NonShared)] 
public class DemoController : Controller 
{ 
    public ActionResult Index() 
    { 
        return View("~/Plugins/Views/Demo/Index.aspx"); 
    } 
}

 The resource cannot be found.
Description: HTTP 404.