I've built this website relying heavily on JQuery, and have run into an issue with IE.
When you click this icon:

There's a custom lightbox that comes down and loads an iframe holding a form. It works fine in Chrome/FF, but in IE it says there's an error:

I've purposely used the non-minified version of JQuery to work out which is the line of code in question, which appears to be:
fx.elem.style[ fx.prop ] = (fx.prop === "width" || fx.prop === "height" ? Math.max(0, fx.now) : fx.now) + fx.unit;
Additionally, this is what I've written to create the lightbox effect:
function popup(url, width, height)
{
var shell = $('<div id="popup-shell"></div>');
shell.append('<div style="margin-top: -' + height + 'px; width: ' + width + 'px; height: ' + height + 'px;" id="popup-inner"></div>');
var inner = shell.find("div#popup-inner");
var cb = $('<a style="margin-left: ' + Number(width - 26) + 'px;" id="popup-close"></a>');
inner.append(cb);
inner.append('<iframe width="' + width + '" height="' + height + '" src="' + url + '" scrolling="no" frameborder="0"></iframe>');
cb.click(function()
{
shell.stop().animate({height: "0%"}, 700, 0, function()
{
shell.remove();
});
});
shell.animate({height: "100%"}, 700, 0, function()
{
inner.animate({marginTop: "120px"}, 700);
});
$("body").append(shell);
}
If this is a known problem, any suggestions or solutions would be great.