title: 500 internal server error when posting
body: <p>in the past few days I started encountering a problem while trying to post to facebook...</p>
  
  <p>For information about my project, I use Unity3D with the social networking plugin from Prime31 for iOS.</p>
  
  <p>Initially, the user is required to login then confirm that the app is allowed to post on the user's timeline.</p>
  
  <p>This happens without flaw and I get response that everything happened properly, until I attempt to post to the timeline. Then I get a 500 internal server error.</p>
  
  <p>here is the error the facebook api gives out:</p>
  
  <pre><code>response error: 500 internal server error
  response text:
  
  Response Headers:
      ACCESS-CONTROL-ALLOW-ORIGIN: *
      EXPIRES: Sat, 01 Jan 2000 00:00:00 GMT
      CONTENT-TYPE: application/json; charset=UTF-8
      WWW-AUTHENTICATE: OAuth "Facebook Platform" "unknown_error" "An unknown error has occurred."
      X-FB-REV: 1102018
      CONNECTION: keep-alive
      PRAGMA: no-cache
      CACHE-CONTROL: no-store
      DATE: Thu, 30 Jan 2014 15:07:54 GMT
      CONTENT-LENGTH: 87
      X-FB-DEBUG: q453qH5ianbIOyeof0X0Ah0PDpAlkxW9+OxLBusy2do=
  </code></pre>
  
  <p>and the function i am using to post to facebook is:</p>
  
  <pre><code>Facebook.instance.postMessageWithLinkAndLinkToImage(Message, URL, URLName, ImageURL, Caption, completionHandler);
  </code></pre>
  
  <p>I do make sure that the user is properly logged in and that the publish permissions have been given.</p>
  
  <p>There has been no code changes with the plugin and my code handling the plugin before and after this issue started to occur, so clearly there is something I am missing. Is this Facebook server's fault? I have already contacted Prime31, but they say that they are not responsible for what the Facebook api responds with.</p>
  
  <p>What can cause 500 internal server error when trying to post to Facebook?</p>
  
  <p>EDIT: it would seem that the postMessageWithLinkAndLinkToImage boils down to:</p>
  
  <pre><code>graphRequest( "me/feed", HTTPVerb.POST, parameters, completionHandler );
  </code></pre>