无法在回调方法中添加视图，并在Windows Phone 7中收到错误“UnauthorizedAccessExcept

我是Windows Phone 7和C#的新手。我遇到导航到新屏幕的问题。我的要求是我需要检查服务器的登录凭据，如果确定，则转到下一个屏幕。但是我收到错误为"未经授权的访问异常" - "无效的跨线程访问"。.

在下面查找代码

 private void button1_Click(object sender, RoutedEventArgs e)
    {     
        HttpWebRequest request = (HttpWebRequest)WebRequest.Create(new Uri(uri));
        request.ContentType = "application/x-www-form-urlencoded";
        request.Method = "POST";
        request.BeginGetResponse(ResponseCallback, request);
    }   
  private void ResponseCallback(IAsyncResult asynchronousResult) 
    {
        var request = (HttpWebRequest)asynchronousResult.AsyncState;
        var response = (HttpWebResponse)request.EndGetResponse(asynchronousResult);
        if (response.StatusCode  == HttpStatusCode.OK)
        {
            this.NavigationService.Navigate(new Uri("/tabview.xaml", UriKind.Relative));
        }
    }