I can see the exact same javascript error on that website:
var sfEls = document.getElementById("mainlevelmainnav").getElementsByTagName("LI");
Looking closer at the issue, it's because you're not displaying your menu with the joomla menu module. Because of that the javascript in the index.php file of the template doesn't find the menu and crash.
You need to remove it:
<script type="text/javascript"><!--//--><![CDATA[//><!--
sfHover = function() {
var sfEls = document.getElementById("mainlevelmainnav").getElementsByTagName("LI");
for (var i=0; i<sfEls.length; i++) {
sfEls[i].onmouseover=function() {
this.className+=" sfhover";
}
sfEls[i].onmouseout=function() {
this.className=this.className.replace(new RegExp(" sfhover\\b"), "");
}
}
}
if (window.attachEvent) window.attachEvent("onload", sfHover);
//--><!]]></script>