Web Api Request.CreateResponse HttpResponseMessage no intellisense VS2012

For some reason, Request.CreateResponse is now "red" in VS2012 and when I hover over the usage the IDE says

Cannot resolve symbol 'CreateResponse'

Here is the ApiController Class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Web.Http.Filters;
using GOCApi.Attributes;
using GOCApi.Models;
using GOCApi.Models.Abstract;
using AttributeRouting;
using AttributeRouting.Web.Http;

namespace GOCApi.Controllers
{
    [RoutePrefix("Courses")]
    public class CoursesController : ApiController
    {
        private ICoursesRepository _coursesRepository { get; set; }

        public CoursesController(ICoursesRepository coursesRepository)
        {
            _coursesRepository = coursesRepository;
        }

        [GET("{id}")]
        public HttpResponseMessage Get(int id)
        {
            var course = _coursesRepository.GetSingle(id);
            if (course == null)
            return Request.CreateResponse(HttpStatusCode.NotFound, "Invalid ID");
            return Request.CreateResponse(HttpStatusCode.OK, course);
        }
    }
}

Granted, the code does compile and works, it's just really annoying seeing all the "red" on my screen. Also, the intellisense doesn't work now when I type Request.CreateResponse. This also used to work, but I started developing other parts to my API and just came back to building controllers so I do not know what happened.

Any thoughts?