weird error with jquery sortable : is not a function

Question

I am getting a weird error when i am using jqueryui sortable. It says,

$(this).sortable(); is not a function.

How to solve this?

edit heres my header code:

<script src="jquery.min.js"></script>
<script src="jquery.ui.core.js"></script>
<script src="jquery.ui.widget.js"></script>
<script src="jquery.ui.mouse.js"></script>
<script src="jquery.ui.sortable.js"></script>

and heres the code i am using to refresh my edit my xml file.

$("#sortable").sortable(
{
    update : function(event, ui) {
        //var change = $(this).sortable('toArray').toString();
        // $('#show').html(change); 
        var order = $(this).sortable('toArray');
        //var order = $(this).val;
    $("#show").load("update_engine_xml.jsp?order="+ order);
        //$("#showid").html(ui.item.context.id+" "+event.target.id);                                            
    }
});

EDIT: 2 any suggestions why i am getting this error?!

Solution

Are you missing a jQuery UI reference?