Error facebook profile picture

Now trying to put the image of the profile of facebook in the ranking of my game.

Watching a tutorial (it's my first project) I wrote this script

 public void QueryScores()
 {
     FB.API ("/app/scores?fields=score,user.limit(30)", Facebook.HttpMethod.GET, ScoresCallback);
 }
 
 private void ScoresCallback (FBResult result)
 {
     Debug.Log ("Scores callback" + result.Text);
     scoresList = Util.DeserializeScores (result.Text);
     
     foreach(Transform child in ScoreScrollList.transform)
     {
         GameObject.Destroy (child.gameObject);
     }
     
     foreach(object score in scoresList)
     {
         var entry = (Dictionary<string,object>) score;
         var user = (Dictionary<string,object>) entry["user"];
         
         
         GameObject ScorePanel;
         ScorePanel = Instantiate (ScoreEntryPanel) as GameObject;
         ScorePanel.transform.parent = ScoreScrollList.transform;
         
         Transform ThisScoreScore = ScorePanel.transform.Find("Friend Score");
         
         Text ScoreScore = ThisScoreScore.GetComponent<Text>();
         
         ScoreScore.text = entry["score"].ToString ();
         
         Transform TheUserAvatar = ScorePanel.transform.Find ("Friend Avatar");
         Image UserAvatar = TheUserAvatar.GetComponent<Image>();
         
         
         FB.API (Util.GetPictureURL(user["id"].ToString (), 128,128), Facebook.HttpMethod.GET, delegate(FBResult pictureResult){
             
             if(pictureResult.Error != null) // if there was an error
             {
                 Debug.Log (pictureResult.Error);
             }
             else // if everything was fine
             {
                 UserAvatar.sprite = Sprite.Create (pictureResult.Texture, new Rect(0,0,128,128), new Vector2(0,0));
             }
             
         });
     }
     
 }

This is the error that gives me and the outcome of the script

Is there anyone who might have no idea how to solve?

Thanks in advance to those who will respond