It's originating from "jquery.nivo.slider.pack.js" and more precisely is complaining about element.data is not a function at line 67 (Firebug is a great tool for such debugging :-) ). I am not entirely sure, but it could be because of the following code in your html:
<script type="text/javascript">
$(window).load(function() {
$('#slider').nivoSlider();
});
</script>
$(window).load will fire as soon as the window is loaded at which point it could be that the slider div is not present in the DOM. So, try changing this to:
<script type="text/javascript">
$(document).ready(function() {
$('#slider').nivoSlider();
});
</script>
This will ensure that the DOM has been painted and available for the plugin to work on. Also, it looks like the plugin expects an 'element' argument, whereas you are passing none, which could be the reason for element.data to be undefined. For this you can try:
$('#slider').nivoSlider($(this));
Hope one of them works for you.