While any developer will be able to fix the error I thought you may want to fix your API documentation for C#. The below will produce a runtime error.

var request = System.Net.WebRequest.Create("http://themoviedb.apiary.io/3/movie/{id}") as System.Net.HttpWebRequest;
request.Method = "GET";
request.Headers.Add("Accept", "application/json");
request.ContentLength = 0;
string responseContent;
using (var response = request.GetResponse() as System.Net.HttpWebResponse) {
  using (var reader = new System.IO.StreamReader(response.GetResponseStream())) {
    responseContent = reader.ReadToEnd();
  }
}

Fix:

var request = System.Net.WebRequest.Create("http://themoviedb.apiary.io/3/movie/{id}") as System.Net.HttpWebRequest;
request.Method = "GET";
request.Accept = "application/json";
request.ContentLength = 0;
string responseContent;
using (var response = request.GetResponse() as System.Net.HttpWebResponse) {
  using (var reader = new System.IO.StreamReader(response.GetResponseStream())) {
    responseContent = reader.ReadToEnd();
  }
}

Or a more complete example

var request = (HttpWebRequest)WebRequest.Create(string.Format("http://api.themoviedb.org/3/movie/{1}?api_key={0}", ApiKey, tmdb));
request.Method = "GET";
request.Accept = "application/json";
request.Headers.Add("Accept-Charset", "UTF-8");
request.ContentLength = 0;
string json;
using (var response = request.GetResponse() as HttpWebResponse)
{
    if (null != response && HttpStatusCode.OK == response.StatusCode)
    {
        using (var reader = new StreamReader(response.GetResponseStream()))
        {
            json = reader.ReadToEnd();
        }
    }
}