We’ve just found that the onload() Javascript event seems to fail to fire from time to time on IE8.  Having done some reasearch there doesn’t seem to be an obvious fix so we’ve decided to reimplement the page but in the meantime to get the page up and running again we’ve added

<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE7"/>

to the meta tags section.  This forces IE8 to use the legacy IE7 rendering engine.  Not exactly a quality fix but enough to keep things running until we can reimplement the page to workaround IE8.  Interestingly the page works perfectly in every other browser we try from IE5 to IE7, FF, Safari etc.