Thickbox not pulling in content in Internet Explorer

I’ve practically finished a very complicated web build with lots of jQuery. All of it working fine in all target browsers. All pages are working fine except for one major issue in Internet Explorer (unsurprisingly)!

I have downloaded a separate version of thickbox and am pulling in the single posts into it from the homepage and the category pages (see code below). However when I try to do this with any version of Internet Explorer, I get the overlay window appearing but with no content inside. The title appears and the window is there but TB_ajaxContent is completely empty with no code just a blank white window.

Why is this only in Internet Explorer? I’m testing in IE8 at the moment but it’s affecting 7 & 9 too. Not even bothering with 6!

<a href="<?php the_permalink() ?>?KeepThis=true&height=450&width=820" title="<?php printf(__('%s', 'veryplaintxt'), wp_specialchars(get_the_title(), 1)) ?>" class="thickbox">

So it’s calling the single.php, if I turn off thickbox it will go to a main parent window version no problem. I have done a process of elimination and systematically turned off al my css one at a time, all my jquery and any plugins.

Is it a specific IE/wordpress issue?

Any help greatly appreciated as it’s the only thing stopping me launching

cheers

Rebekah