i think the progress bar script is conflicting with your /html5shiv.js script. try addinbg a conditional so it is not included for IE 8
<!--[if lt IE 9]>
<script src="assets/js/html5shiv.js"></script>
<script src="assets/js/respond.min.js"></script>
<![endif]-->
<!--[if gte IE 9]>
<script src="webassist/progress_bar/jquery-blockui-formprocessing.js" type="text/javascript"></script>
<![endif]-->