[jQuery] Treeview and IE "object doesn't support this object or method"

[cfdvlpr]

I'm getting this error in IE, but not Firefox.
It borks on this line: $("#pageNav").Treeview({speed: "fast",
collapsed: true, openurl: true});

        <script type="text/javascript" src="/jquery/plugins/
jquery.treeview.js"></script>
        <script type="text/javascript">
                $(function(){
                        $("#pageNav").Treeview({speed: "fast", collapsed: true, 
openurl:
true});
                        $("#pageNav").show();
                });
        });
        </script>

Any idea what causes this error?