trying to use an imagebutton control to display fancybox (open a page) with parameter once clicked

seems it did not work with the following :

function RegisterFancyLinks() {
            $('iframe').fancybox({
                overlayShow: true,
                overlayColor: '#B2B2B2'
            });

        $(function () {
            var ajaxMng = Sys.WebForms.PageRequestManager.getInstance();
            ajaxMng.add_endRequest(RegisterFancyLinks);

            RegisterFancyLinks();
        });

 <asp:ImageButton ID="ibViewCustomerCredit" runat="server" ImageUrl="~/images/transmagglass.png" CssClass="iframe" />

if (cus.CustomerCode != "")
  {
       ibViewCustomerCredit.PostBackUrl = "InvoiceRatingSummary.aspx?customercode=" + strCustomerDetails[0].ToString();
  }