wp8 app crash

gistfile1.cs

// App exits on call to client.UploadStringAsync
// The ClientUploadStringCompleted handler is never called.

public event EventHandler<LoginCompletedEventArgs> LoginCompleted;
public void OnLoginCompleted(LoginCompletedEventArgs e)
{
    var handler = LoginCompleted;
    if (handler != null) handler(this, e);
}

// GeoVision lamely authenticates with username/pw in the clear in the POST body
// At least we can use SSL.
// At https://host:port/phoneinfo is an HTML doc that lists the cameras, which is
public void Login(String host, int port, bool ssl, String userName, String password,
                  EventHandler<LoginCompletedEventArgs> loginCompletedEventHandler) {
    LoginCompleted += loginCompletedEventHandler;
    // stash away the base URL
    _url = String.Format("{0}://{1}:{2}", ssl ? "https" : "http", host, port);
    var formData = String.Format("id={0}&pwd={1}&ImageType=1", userName, password);
    var client = new WebClient();
    client.UploadStringCompleted += ClientUploadStringCompleted;
    client.UploadStringAsync(new Uri(_url + "/phoneinfo"), formData);
}

private void ClientUploadStringCompleted(object sender, UploadStringCompletedEventArgs e) {
    ObservableCollection<GeoVisionCamera> cameras = null;
    Exception ex = null;
    if (e.Error != null) {
        ex = e.Error;
    }
    else {
        var htmlDoc = new HtmlDocument();
        htmlDoc.LoadHtml(e.Result);
        cameras = new ObservableCollection<GeoVisionCamera>();
        var nodes = htmlDoc.DocumentNode.SelectNodes("//a");
        if (nodes == null) {
            ex = new Exception("Error parsing html");
            var h2 = htmlDoc.DocumentNode.SelectSingleNode("//h2");
            if (h2 != null)
                ex = new Exception(h2.InnerText.Trim());
        }
        else {
            // get all but last (it's not a camera)
            for (int i = 0; i < nodes.Count - 1; i++) {
                var name = nodes[i].InnerText.Trim();
                var url = nodes[i].GetAttributeValue("href", "");
                var jpgUrl = String.Format("{0}/{1}/cam{2}.jpg", _url,
                                           url.Substring(url.IndexOf("IDKey=", StringComparison.Ordinal) + 6, 36),
                                           i);
                cameras.Add(new GeoVisionCamera(name, i, jpgUrl));
            }
        }
    }

    var args = new LoginCompletedEventArgs(ex, cameras);
    OnLoginCompleted(args);
}