first add new button and set it TargetControlID
<asp:ImageButton ID="ImageButton2" runat="server" onclick="ImageButton2_Click"
style="position:absolute; top: 175px; left: 523px;"
ImageUrl="~/pics/programs.jpg" />
<asp:Panel ID="pnlprog" runat="server" BackImageUrl="~/pics/programs pop.jpg" Width="800px" Height="500"
HorizontalAlign="NotSet" style="display:none; padding=0px;" BorderColor="Black" BorderStyle="None" BorderWidth="1px">
<asp:LinkButton ID="blk" runat="server" Text="* Balakuteer (Orphanage)" OnClick="blk_click" style="position:absolute; top:90px; left:590px;" Font-Size="Medium" ForeColor="#69A4B0" Font-Underline="False" Font-Bold="True"></asp:LinkButton>
</asp:Panel>
<asp:button runat="server" id="btnShowModalPopup" style="display: none" xmlns:asp="#unknown" />
<ajaxtoolkit:ModalPopupExtender ID="mdlPopupProg" BehaviorID="mdlPopupProg" runat="server" TargetControlID="btnShowModalPopup" PopupControlID="pnlprog" OkControlID="hlprog" BackgroundCssClass="modalBackground" />
<mb:ModalPopupAnimationExtender ID="ModalPopupAnimationExtender2"
runat="server" ModalPopupBehaviorID="mdlPopupProg" TargetControlID="pnlprog">
<Animations>
<OnShown>
<FadeIn Duration="1.5" Fps="20" />
</OnShown>
</Animations>
</mb:ModalPopupAnimationExtender>
then
show ModalPopupExtender on server site:
write on click event of ImageButton2
ModalPopupExtender1.Show();