To be more clear, the fix for me works on every browser for my test site at www.mygamedemos.com/store. However, with the same setup, it doesnt work on Internet Explorer 8.0.6001.18702 for my main site www.cocobeau.co.uk
Accessed your live site with IE 8.0.6001.18702. Can safely report that you have no problem with your zen lightbox setup.
Try clearing your cache and browser history and try again.