How can I parse the following JSON for WP7 and bind to a listbox?

I'm having some trouble binding this json to a ListBox...The problem seems to happen in the ActivityTrack class/object of the JSON...i'm not sure what is not meshing...

{"collection":[{"type":"track","created_at":"2011/09/18 14:04:00 +0000","origin":{"id":23606164,"created_at":"2011/09/18 14:03:59 +0000","user_id":222927,"duration":342465,"commentable":true,"state":"finished","sharing":"public","tag_list":"garage usgarage soulfulhouse house deephouse deep","permalink":"pablo-cortez-when-i-need-u","description":"","streamable":true,"downloadable":false,"genre":"UK Garage","release":"","purchase_url":null,"label_id":null,"label_name":"","isrc":"","video_url":null,"track_type":"demo","key_signature":"","bpm":null,"title":"Pablo Cortez - When I Need U (Back To 90s Mix)","release_year":null,"release_month":null,"release_day":null,"original_format":"mp3","license":"all-rights-reserved","uri":"https://api.soundcloud.com/tracks/23606164","permalink_url":"http://soundcloud.com/pablocortez/pablo-cortez-when-i-need-u","artwork_url":null,"waveform_url":"http://w1.sndcdn.com/wuiZilHRZhl6_m.png","user":{"id":222927,"permalink":"pablocortez","username":"Pablo Cortez","uri":"https://api.soundcloud.com/users/222927","permalink_url":"http://soundcloud.com/pablocortez","avatar_url":"http://i1.sndcdn.com/avatars-000000771958-y059w8-large.jpg?ca13f03"},"stream_url":"https://api.soundcloud.com/tracks/23606164/stream","user_playback_count":1,"user_favorite":false,"playback_count":28,"download_count":0,"favoritings_count":0,"comment_count":2,"attachments_uri":"https://api.soundcloud.com/tracks/23606164/attachments","sharing_note":{"text":"My new sounds","created_at":"2011/09/18 14:03:59 +0000"}},"tags":"affiliated"}],"next_href":"https://api.soundcloud.com/me/activities/track.json?cursor=86db5e5e-e1fe-11e0-9c69-0f0dad493cfc\\u0026limit=1","future_href":"https://api.soundcloud.com/me/activities/track?uuid%5Bto%5D=2d9c67ee-e22f-11e0-94fa-45aa16adeba3"}

Here is the class structure which i am trying to bind the JSON too

public class Activities
{
    public ActivityTrack [] activities { get; set; }
    public string next_href { get; set; }
    public string future_href { get; set; }
}

public class ActivityTrack
{
    public string type { get; set; }
    public string created_at { get; set; }
    public OriginActivityTrack origin { get; set; }
    public string tags { get; set; }
}

public class OriginActivityTrack
{
    public string id { get; set; }
    public string created_at { get; set; }
    public string user_id { get; set; }
    public string duration { get; set; }
    public string commentable { get; set; }
    public string state { get; set; }
    public string sharing { get; set; }
    public string tag_list { get; set; }
    public string permalink { get; set; }
    public string description { get; set; }
    public string streamable { get; set; }
    public string downloadable { get; set; }
    public string genre { get; set; }
    public string release { get; set; }
    public string purchase_url { get; set; }
    public string label_id { get; set; }
    public string label_name { get; set; }
    public string isrc { get; set; }
    public string video_url { get; set; }
    public string track_type { get; set; }
    public string key_signature { get; set; }
    public string bpm { get; set; }
    public string title { get; set; }
    public string release_year { get; set; }
    public string release_month { get; set; }
    public string release_day { get; set; }
    public string original_format { get; set; }
    public string license { get; set; }
    public string uri { get; set; }
    public string permalink_url { get; set; }
    public string artwork_url { get; set; }
    public string waveform_url { get; set; }
    public SmallUser user { get; set; }
    public string stream_url { get; set; }
    public string user_playback_count { get; set; }
    public str开发者_JAVA技巧ing user_favorite { get; set; }
    public string playback_count { get; set; }
    public string download_count { get; set; }
    public string favoritings_count { get; set; }
    public string comment_count { get; set; }
    public string attachments_uri { get; set; }
    public SharingNote sharing_note;
}

public class SharingNote
{
    public string text { get; set; }
    public string created_at { get; set; }
}

public class SmallUser
{
    public string id { get; set; }
    public string permalink { get; set; }
    public string username { get; set; }
    public string uri { get; set; }
    public string permalink_url { get; set; }
    public string avatar_url { get; set; }
}

This is the current code for binding to listbox:

private void ReadCallbackDashboard(IAsyncResult asynchronousResult)
{
    lock (locker)
    {
        try
        {
            HttpWebRequest request =
              (HttpWebRequest)asynchronousResult.AsyncState;
            HttpWebResponse response =
              (HttpWebResponse)request.EndGetResponse(asynchronousResult);
            using (StreamReader streamReader1 =
              new StreamReader(response.GetResponseStream()))
            {
                string resultString = streamReader1.ReadToEnd();

                using (var ms = new MemoryStream(Encoding.Unicode.GetBytes(resultString)))
                {
                    if (ms != null)
                    {
                        var ser = new DataContractJsonSerializer(typeof(Activities));
                        Activities obj = (Activities)ser.ReadObject(ms);
                        userDashboardActivities = null;


                        userDashboardActivities = new ObservableCollection<ActivityTrack>();
                        for (int i = 0; i < obj.activities.Length; ++i)
                        {

                                userDashboardActivities.Add(obj.activities[i]);

                        }

                        if (userDashboardActivities.Count() == 0)
                        {
                            messageDashboard = "No Tracks Found";
                            UIThread.Invoke(() => mainMessage.Text = messageDashboard);
                        }
                        else
                        {
                            messageDashboard = "";
                            UIThread.Invoke(() => mainMessage.Text = messageDashboard);
                            UIThread.Invoke(() => dashboardBox.ItemsSource = userDashboardActivities);
                        }
                    }
                }
            }
        }
        catch (WebException we)
        {
            UIThread.Invoke(() => MessageBox.Show("Could not retrieve the latest. Internet down? Try a refresh."));
        }
    }
}

please check it out! Thanks in advance!

Answer as discovered in the comments.

You have called your property activities but the json calls it collection.