ModalPopUpExtender in a GridView

I am using ModalpopExtender to show  a popup window when the user clicks on the one of the Row.

I dont know where I am doing mistake Its not working for me .

I am getting error TargetControlId is not found.

I am using VS2008 with C#

Here is my code.
Thanks in Advance

<asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
 
<asp:GridView ID="MyTable"  AllowPaging="false" AutoGenerateColumns="false" runat="server">
    <Columns>
        <asp:TemplateField>           
            <ItemTemplate>
                <a href='http:\\www.yahoo.com' id="lnkName"><%=Name%></a>
               <cc1:ModalPopupExtender ID="ModalPopup1" runat="server" TargetControlID="lnkName"
                PopupControlID="pnlpopup" BackgroundCssClass="modalBackground" DropShadow="true"
                OkControlID="btnYes" CancelControlID="CancelBtn" />           
              <asp:Panel ID="pnlpopup" runat="server" CssClass="modalPopup" Style="display:none"
                Width="278px" Font-Names="@MS PGothic">
    Hi Would you like to Take a survey    
                <asp:Button ID="btnYes" runat="server" Text="Yes" />                
                <asp:Button ID="CancelBtn" runat="server" Text="Cancel" Width="52px" />
            </asp:Panel>
            </ItemTemplate>
        </asp:TemplateField>            
    </Columns>
</asp:GridView>

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