Can Anyone Help me about This Coding....I hv to Insert a data in table via ADO.NET web services.(

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using demo1.ServiceReference1;
using System.Data.Services.Client;
using System.Xml.Linq;
using System.Xml;
using System.ComponentModel;
using System.IO.IsolatedStorage;
using System.IO;
using System.Collections.ObjectModel;

namespace demo1
{
    public partial class MainPage : UserControl
    {
    Database1Entities de = new Database1Entities(new Uri("WebDataService1.svc", UriKind.Relative));
    ObservableCollection<Table1> ob = new ObservableCollection<Table1>();

    ObservableCollection<Table1> obs;

    public MainPage()
    {
        InitializeComponent();
    }

    private void btn_add_clk(object sender, System.Windows.RoutedEventArgs e)
    {
        Table1 tb = new Table1();

        tb.name = txt_name.Text;
        tb.address = txt_name_address.Text;
        de.AddToTable1(tb);
        de.BeginSaveChanges(onsave, tb);
    }

    void onsave(IAsyncResult re)
    {
        de.EndSaveChanges(re);  <==[error]{ Data servuce Requet exceptoons was unhabdked by User code}
        ob.Add(re.AsyncState as Table1);
        grid_show.UpdateLayout();

    }

can any one tell me Why i got this error........... & can u tell me how can i learn this code via Online tutorial..Please send me link,.....

thanks in Advance,,,