Disappearing jump menus in IE

[Cyroq]

I'm not this if this is a CSS problem, but I'm guessing it is.
I have created a quite complex website, with lots of javascript and Leightbox (a variation on Lightbox). Inside the leightbox container there is a form, with checkboxes and jump menus. When the box is being opened, everything works fine in Firefox, Chrome etc. In IE the box opens, but somehow the jump menus disappear. The checkboxes stay visible though
If I set the leightbox display status to 'block' manually (so the website loads with the leightbox popped up already) there is no problem.

Since only the jump menus disappear I'm quite confused what could be the problem. Is there anyone who might know what's causing this? If neccessary, I can post some more code.

Leightbox css:

.leightbox {
	color: #333;
	display: none;
	position: absolute;
	top: 25%;
	left: 25%;
	width: 800px;
	height: 1000px;
	padding: 1em;
	border: 1em solid #333;
	background-color: #FFFCE1;
	text-align: left;
	z-index:1001;
	overflow: auto;
}

[Kor]

post a link to a test page. And tell us which browser does that. All?

[Cyroq]

You can find it here: http://www.bbsuripakkettencateringse...lot/index.html. Hit one of the items on the left menu and hit the 'Bestellen' button. In IE (Internet Explorer) I don't see the jump menus, in Firefox and Chrome I do.
I hope you can understand the structure of the website, it's quite complicated

[Kor]

All I can see is that is either a problem of CSS visibility or z-index. In IE8 the select elements have visibility:hidden. In IE7 the whole light box is covered by the gray transparent div. It is hard to say where is the error...

[Cyroq]

Damn, that's going to be hard to solve. It's strange that the jumpmenus and checkboxes have different visibilities, as far as I know they are treated equally.
Maybe I can find another way to create the lightbox effect with a div in the box.