title: Access method 'Facebook.HttpHelper.UrlDecode(System.String)' failed - WinPhone8
body: <p>I've installed the latest Facebook.Client package to try and integrate facebook on my Windows Phone 8 game. The connection to log in is fine but upon trying to return to the game app, I get the following error message: </p>
  
  <p>"Attempt by method 'Facebook.Client.AppAuthenticationHelper.GetQueryStringValueFromUri(System.String, System.String)' to access method 'Facebook.HttpHelper.UrlDecode(System.String)' failed."</p>
  
  <p>The Facebook package is present in my solution (installed as a dependency of Facebook.Client, if memory serves), but this does not appear to have an HttpHelper class.</p>
  
  <p>Can anyone advise on what I need to get this working?</p>
  
  <p>Thanks.</p>