I have a webapi project running rc

I have a very basic controlller like

 [System.Web.Http.HttpPost]
    public void Update(Business business)
    {
        //if (business.Id == Guid.Empty)
        //{
        //    throw new HttpResponseException("Business ID not provided", HttpStatusCode.BadRequest);
        //}

         _repository.Update(business);
        //if (!isUpdated)
        //{
        //    throw new HttpResponseException("Business not found", HttpStatusCode.NotFound);
        //}
    }

I found an example using HttpClient however it doesnt work with rc

    using (var client = new HttpClient())
        {
            try
            {
               string url = string.Format("{0}{1}", ConfigurationManager.AppSettings["ApiBaseUrl"].ToString(),apiMethod);

                HttpRequestMessage request = new HttpRequestMessage();
                MediaTypeFormatter[] formatter = new MediaTypeFormatter[] { new JsonMediaTypeFormatter() };

                var content = request.CreateContent<Business>(
                    business, 
                    MediaTypeHeaderValue.Parse("application/json"),
                    formatter, new FormatterSelector());
                HttpResponseMessage response = client.PostAsync(url, content).Result;
                return response.Content.ToString();
            }
            catch (Exception ex)
            {
                return null;
            }

        }

I get an error

Method not found: 'Void System.Net.Http.Headers.HttpHeaders.AddWithoutValidation(System.String, System.String)'.

Passing the data from jquery is a piece of cake however I need call the api from code behind vs client side.

Can someone point me in the right direction for calling the webapi?

Thank you