The nav
tag is not supported in IE 8 and below, to circumvent this simply include an HTML5 shim that would add support for those tags which are breaking. Try adding this in the <head>
section of your page:
<!-- HTML5 shim, for IE6-8 support of HTML5 elements -->
<!--[if lt IE 9]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->