GIF image in modal Popup not working

<ajax:ModalPopupExtender ID="mpeLoading" runat="server" PopupControlID="ajaxProcessPopupPanel"
BackgroundCssClass="overlay" TargetControlID="hdnPopup2" DropShadow="false" Drag="false">

<asp:Panel ID="ajaxProcessPopupPanel" runat="server" Style="display: none;">

<table cellpadding="0" cellspacing="0" border="0" class="tblpopup">
<tr>
<td align="center">
<asp:Label ID="lblProcessing" runat="server" Text="Processing ..." Font-Bold="true"
ForeColor="Green">
</td>
</tr>
<tr>
<td align="center">
<asp:Image ID="imgLoad" runat="server" ImageUrl="~/Images/ajax-loader.gif" />
</td>
</tr>
</table>

This is my code