title: get an access token using Facebook C# SDK
body: <p>Hi i am using the following code to get access token from facebook using C# SDK</p>
  
  <pre><code>var fb = new FacebookClient();
      dynamic result = fb.Get("oauth/access_token", new
      {
          client_id = "clientId",
          client_secret = "clientSecret",
          redirect_uri = "redirectUri",
          code = "code"
      });
  
      return result.access_token;
  </code></pre>
  
  <p>the above code works perfect most of the time but some times i gets this error </p>
  
  <pre><code>(OAuthException - #100) Invalid verification code format.
  </code></pre>
  
  <p>how to fix this problem??</p>