gridview paging not displaying second page.

Hi,
I am using below mentioned code to display data into gridview. it is showing data of first page excellent. When I clicked on 2 page or any other page the gridview disappear to the web page and webpage blank.
Please help me where I am doing wrong/

 <asp:GridView ID="Invoicing" runat="server" AutoGenerateColumns="False"
        HeaderStyle-Font-Size="Medium" HeaderStyle-Font-Italic="true" CellPadding="1"
        ForeColor="#333333" GridLines="None" Width="908px"
        AllowPaging="True" PageSize="12" AllowSorting="True" EnableSortingAndPagingCallbacks="True"
        OnPageIndexChanging="Invoicing_PageIndexChanging" >       
        <AlternatingRowStyle BackColor="White" ForeColor="#284775" />


 public partial class InvPage : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            loadGrid();
        }
        SqlConnection con;
        SqlCommand cmd;
        DataSet ds;
        SqlDataAdapter da;
                   
        private void loadGrid()
        {
             string values = "Select sno=Row_number() Over (Order by InvNo,Date), Date, InvNo, Amt=Sum(Amt), CoCom=Sum(Isnull(CoCom,0)), MkCom=Sum(Isnull(MkCom,0)), NPV=Sum(NetPurchasedValue), FreeStock from tempp Where FreeStock='0' Group by Date, InvNo, FreeStock Order by InvNo,Date";
               
            using (con = new SqlConnection(ConfigurationManager.ConnectionStrings["DLICCBPL"].ConnectionString))
            {
                cmd = new SqlCommand(values,con);
                con.Open();                
                ds = new DataSet();
                da = new SqlDataAdapter(cmd);
                da.Fill(ds,"bb");
                Invoicing.DataSource = ds;
                Invoicing.DataMember = "bb";                
                Invoicing.DataBind();

               
                con.Close();
               
            }
        }

        protected void Invoicing_PageIndexChanging(Object sender, GridViewPageEventArgs e)
        {
            Invoicing.PageIndex = e.NewPageIndex;
            Invoicing.DataBind();
            //((GridView)sender).PageIndex = e.NewPageIndex;

           
        }
       

    }