Progress bar usign gif image untill next panel opens.

<style type="text/css">
.modalPopup
{
background-color: #696969;
filter: alpha(opacity=40);
opacity: 0.7;
xindex:-1;
}
</style>

<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server"/>

<script type="text/javascript">
    var prm = Sys.WebForms.PageRequestManager.getInstance();
    //Raised before processing of an asynchronous postback starts and the postback request is sent to the server.
    prm.add_beginRequest(BeginRequestHandler);
    // Raised after an asynchronous postback is finished and control has been returned to the browser.

    prm.add_endRequest(EndRequestHandler);
    function BeginRequestHandler(sender, args) {
        //Shows the modal popup - the update progress
        var popup = $find('<%= modalPopup.ClientID %>');
        if (popup != null) {
            popup.show();
        }
    }

    function EndRequestHandler(sender, args) {
        //Hide the modal popup - the update progress
        var popup = $find('<%= modalPopup.ClientID %>');
        if (popup != null) {
            popup.hide();
            //alert("hi");
        }
    }
</script>
<div>
<asp:UpdateProgress ID="UpdateProgress" runat="server">
<ProgressTemplate>
<asp:Image ID="Image1" ImageUrl="~/Images/animations-photoshop-26.gif" AlternateText="Processing" runat="server" />
</ProgressTemplate>
</asp:UpdateProgress>
<asp:modalpopupextender id="modalPopup" runat="server" TargetControlID="UpdateProgress" PopupControlID="UpdateProgress" BackgroundCssClass="modalPopup" />

<asp:UpdatePanel ID="pnlData" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:Button ID="btnSubmit" runat="server" Text="Submit" onclick="btnSubmit_Click"/>
    <asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>
</div>
</form>