i found the solution is that we can remove the iframe containing div id learn_more on popup window close button and then below that we append the div id learn_more with iframe.it means on close we delete the iframe div and same time we create the div with iframe. like this
BTNClose.click(function () {
$(this).find(".AeroWindow").css('display', 'block');
var sdx= $('#cboxLoadedContent div').find('div.AeroWindow ui-draggable active');
$('#cboxLoadedContent div').find('div.AeroWindow').removeClass('.active ui-draggable');
$('#learn_more').remove();
$('#cboxLoadedContent div').find('div#learn').append("<div id='learn_more' style='display: none; width: 100%; height: 100%;'><iframe width='100%' height='100%' frameborder='0' scrolling='yes' marginheight='0' marginwidth='0' src='window_page-price_learn_more' align='bottom'></iframe></div>")
$('.AeroWindow ui-draggable active').remove();
WindowContent="";
Window.css('display','none');
return(false);
});