[C# net 4] Load page please wait (not updating but page load)

Hi all, hope in your help and suggestions.

I need show the classic message 'Please wait' when my gridview is populated in my page aspx.

In the google search I find all examples and tutorials with buttons that update the page aspx, e.g.:
http://aspsnippets.com/Articles/Disp...ng-ASPNet.aspx

In this demo when call gridview.aspx the message not show, instead is show when click in the button 'btnSubmit'.

Can you help me?

I tried this version but the images spinner4-greenie.gif not showed:

Code:
<body>
    <form id="form1" runat="server">
    <ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager1" runat="server">
    </ajaxToolkit:ToolkitScriptManager>
    <div>
        <asp:UpdatePanel ID="UpdatePanel1" runat="server">
            <ContentTemplate>
                <asp:GridView ID="DecoderView" runat="server" AllowPaging="True" AllowSorting="true"
                    AutoGenerateColumns="False" PageSize="13" ShowHeader="true" OnPageIndexChanging="GridView1_PageIndexChanging"
                    OnRowDataBound="GridView1_RowDataBound" CssClass="mGrid" ShowHeaderWhenEmpty="true"
                    EmptyDataText="No data available." DataKeyNames="ID" OnRowEditing="GridView1_RowEditing"
                    OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowCommand="GridView1_RowCommand"
                    OnRowUpdating="GridView1_RowUpdating" OnRowDeleting="GridView1_RowDeleting">
                    <Columns>
                    ...
                    </Columns>
                </asp:GridView>
            </ContentTemplate>
        </asp:UpdatePanel>
        <br />
        <asp:UpdateProgress ID="UpdateProgress1" runat="server">
            <ProgressTemplate>
                <div class="loading" align="center">
                    <img src="images/spinner4-greenie.gif" alt="" />
                </div>
            </ProgressTemplate>
        </asp:UpdateProgress>
    </div>
    </form>
</body>