I've upgraded to vB3.0.1 and no probs ...
One more suggestion - change the javascript in vbulletin_chgclass.js to match this (it's one letter different):
HTML Code:
<!--
function changeSty(classpassed,elementid){
document.getElementsById(""+elementid+"").className=""+classpassed+"";
}
//-->
Let me know how you go - seems to work either way for me ... the functions are translatable in Javascript 1.1 - but like I've said, I've not had problems with the original script - so the only way I can really help more is to take a look @ your board - which I will do