WWW zero sized post buffer error Standalone

Hi

When I try to make a WWW request via a WWWForm I allways get an error saying: "You are trying to load data from a www stream which had the following error when downloading. Error when creating request. POST request with a zero-sized post buffer is not supported. UnityEngine.WWW:get_text()" This however only happens if the Platform in the Build Settings is set to "PC and MAC Standalone". If I switch the platform to Web Player everything works perfectly. Anyone an idea what might be causing this? Thx in advance.

 private void MakeRequest(Uri url, HttpVerb httpVerb,
                                Dictionary<string, string> args, Action<JsonData> method)
     {
         string requestString = url.ToString();

         if (args != null && args.Keys.Count > 0 && httpVerb == HttpVerb.GET)
         {
             requestString += EncodeDictionary(args, true);
         }

         WWWForm form = new WWWForm();

         // Create a download object
         download = new WWW(requestString, form);

         if(method != null)
             StartCoroutine(WaitForDownload(download, method));
     }

     private IEnumerator WaitForDownload(WWW download, Action<JsonData> method)
     {
         yield return download;

         JsonData data;

         if (download.error == null)
         {
             Debug.Log(download.text);
             data = JsonMapper.ToObject(download.text);
         }
         else
         {
             Debug.Log(download.error);

             string error = "{\"" + "error\"" + " : " + "\"" + download.error + "\"" + "}";
             Debug.Log(error);
             data = JsonMapper.ToObject(error);
         }

         if(method != null)
             method(data);
     }