System.web.mvc.modelstatedictionary does not contain a definition for addruleviolations

I am getting two errors when trying to build NerdDinner in DinnerController.cs. Here is what I currently have in DinnerController.cs. I am getting errors on the two lines with '**'

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web; 
using System.Web.Mvc;
using NerdDinner.Models;



namespace NerdDinner.Controllers
{
public class DinnersController : Controller
{
    DinnerRepository dinnerRepository = new DinnerRepository();

    //
    // GET: /Dinners/
    public ActionResult Index()
    {

        var dinners = dinnerRepository.FindUpcomingDinners().ToList();
        return View(dinners);
    }

    //
    // GET: /Dinners/Details/2

    public ActionResult Details(int id)
    {

        Dinner dinner = dinnerRepository.GetDinner(id);

        if (dinner == null)
            return View("NotFound");
        else
            return View(dinner);
    }

    //
    // GET: /Dinners/Edit/2

    public ActionResult Edit(int id)
    {

        Dinner dinner = dinnerRepository.GetDinner(id);
        return View(dinner);
    }

    //
    // POST: /Dinners/Edit/2

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Edit(int id, FormCollection formValues)
    {

        Dinner dinner = dinnerRepository.GetDinner(id);

        try
        {
            UpdateModel(dinner);

            dinnerRepository.Save();

            return RedirectToAction("Details", new { id = dinner.DinnerID });
        }
        catch
        {
            **ModelState.AddRuleViolations(dinner.GetRuleViolations());

            return View(dinner);
        }
    }

    //
    // GET: /Dinners/Create

    public ActionResult Create()
    {

        Dinner dinner = new Dinner()
        {
            EventDate = DateTime.Now.AddDays(7)
        };
        return View(dinner);
    }

    //
    // POST: /Dinners/Create

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create(Dinner dinner)
    {

        if (ModelState.IsValid)
        {

            try
            {
                dinner.HostedBy = "SomeUser";

                dinnerRepository.Add(dinner);
                dinnerRepository.Save();

                return RedirectToAction("Details", new { id = dinner.DinnerID });
            }
            catch
            {
                ** ModelState.AddRuleViolations(dinner.GetRuleViolations());
            }
        }

        return View(dinner);
    }

    //
    // HTTP GET: /Dinners/Delete/1

    public ActionResult Delete(int id)
    {

        Dinner dinner = dinnerRepository.GetDinner(id);

        if (dinner == null)
            return View("NotFound");
        else
            return View(dinner);
    }

    //
    // HTTP POST: /Dinners/Delete/1

    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Delete(int id, string confirmButton)
    {

        Dinner dinner = dinnerRepository.GetDinner(id);

        if (dinner == null)
            return View("NotFound");

        dinnerRepository.Delete(dinner);
        dinnerRepository.Save();

        return View("Deleted");
    }
}
}

Any help is greatly appreciated.

Have you created the Nerd Dinner Helper Class in the Helper Directory as below? I Think I had this issue when I was at that stage...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using NerdDinner.Models;

namespace NerdDinner.Helpers {

    public static class ModelStateHelpers {

        public static void AddModelErrors(this ModelStateDictionary modelState, IEnumerable<RuleViolation> errors) {

            foreach (RuleViolation issue in errors) {
                modelState.AddModelError(issue.PropertyName, issue.ErrorMessage);
            }
        }
    }
}