WWW.Post works fine in Editor, but not in WebPlayer Build

here is my post request to server: public WWW POST(string url, string post) { var www = new WWW(url, Encoding.UTF8.GetBytes(post));

     StartCoroutine(WaitForRequest(www));
     while (!www.isDone && www.error == null)
     {
         Console.Write("downloading...");
         Thread.Sleep(1000);
     }
     return www;
 }
 
 private IEnumerator WaitForRequest(WWW www)
 {
     while (!www.isDone && www.error == null) { yield return new WaitForSeconds(0.1f);}
 
     // check for errors
     if (www.error != null)
     {
         Debug.Log("WWW Error: " + www.error);
     }
 }

it works fine in Unity Editor, but it freeze to unlimited loop in Web Player Build version. Does anybody know why?