ASP.NET MVC Forms code challenge Redirect() not working even though System.Web.Mvc using statement is included.

using System.Web.Mvc;
using IssueReporter.Data;
using IssueReporter.Models;

namespace IssueReporter.Controllers
{
    public class IssuesController : Controller
    {
        private IssuesRepository _issuesRepository;

        public IssuesController()
        {
            _issuesRepository = new IssuesRepository();
        }

        public ActionResult Index()
        {
            return View();
        }

        public ActionResult Report()
        {
            var issue = new Issue();

            return View(issue);
        }

        [HttpPost]
        public ActionResult Report(Issue issue)
        {
            if (ModelState.IsValid)
            {
                _issuesRepository.AddIssue(issue);
                return Redirect("Index");
            }

            return View(issue);
        }
    }
}