problem creating a auto complete textbox using jquery,json and asp.net

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Hi I am not able to understand where I am going wrong in creating auto fill textbox.

Here is my jquery code:

function BindTexbox(data) {
            debugger;
            var availableTags = [
      "ActionScript",
      "AppleScript",
      "Asp",
      "BASIC",
      "C",
      "C++",
      "Clojure",
      "COBOL",
      "ColdFusion",
      "Erlang",
      "Fortran",
      "Groovy",
      "Haskell",
      "Java",
      "JavaScript",
      "Lisp",
      "Perl",
      "PHP",
      "Python",
      "Ruby",
      "Scala",
      "Scheme"
    ];   
            $("#txt_membrid_name").autocomplete({
                source: availabletags
            });




        }

And this is my HTML Markup

<input type="text" id="txt_membrid_name" class="tb" onkeyup="GetTxtBoxVal();" />

everything works fine. I get respone from my onkey up event and on success I enter into BindTexbox(data).
Somehow my code wasn't working so I tried with dummy array ie; availabletags.
But every time I am geting this error autocomplete is not a method defined.

I am using following js files:

<script src="../../Scripts/Core/jquery-ui.js" type="text/javascript"></script>
    <script src="../../Scripts/JS_UI_Effects/jquery.ui.widget.js" type="text/javascript"></script>
    <script src="../../Scripts/JS_UI_Effects/jquery-ui-1.8.7.custom.min.js" type="text/javascript"></script>
    <script src="../../Scripts/Core/jquery-1.8.3.js" type="text/javascript"></script>
    <script src="../../Scripts/Core/jquery.ui.autocomplete.js" type="text/javascript"></script>
    <link href="../../Styles/Content/themes/base/jquery.ui.autocomplete.css" rel="stylesheet"
        type="text/css" />

Please tell me where I am going wrong and how to rectify it. I am new in JQuery.

Many Thanks.

Taresh