In the following code I get an error that says autocomplete function Object is not a property or method

Here is the code:

<title><%= ViewData["pagetitle"] + " | " + config.Sitename.ToString() %></title>
    <script src="../../Scripts/jqueryui/jquery-ui-1.8.1.custom/development-bundle/ui/minified/jquery.ui.core.min.js"
        type="text/javascript"></script>
    <script src="../../Scripts/jqueryui/jquery-ui-1.8.1.custom/development-bundle/ui/minified/jquery.ui.core.min.js"
        type="text/javascript"></script>

    <script src="../../Scripts/jqueryui/jquery-ui-1.8.1.custom/development-bundle/ui/jquery.ui.widget.js"
        type="text/javascript"></script>

    <script src="../../Scripts/jqueryui/jquery-ui-1.8.1.custom/development-bundle/ui/jquery.ui.position.js"
        type="text/javascript"></script>

    <script src="../../Scripts/jqueryui/jquery-ui-1.8.1.custom/development-bundle/ui/jquery.ui.autocomplete.js"
        type="text/javascript"></script>
    <script language="javascript" type="text/javascript" src="/Scripts/main.js"></script>

    <script language="javascript" type="text/javascript">
        $(document).ready(function () {

            Categories();

            $('#tags1').autocomplete({ //error here
                url: '/Tag/TagAutoComplete',
                width: 320,
                max: 4,
                delay: 30,
                cacheLength: 1,
                scroll: false,
                highlight: false
            });

        });

    </script>