'JQuery' is undefined

<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<script src="../../Scripts/MicrosoftAjax.debug.js" type="text/javascript"></script>

<script src="../../Scripts/MicrosoftMvcAjax.debug.js" type="text/javascript"></script>

<script src="../../Scripts/jquery-1.2.6.js" type="text/javascript"></script>

<!-- YUI Styles -->
<link href="../../Content/reset.css" rel="stylesheet" type="text/css" />
<link href="../../Content/fonts.css" rel="stylesheet" type="text/css" />
<link href="../../Content/grids.css" rel="stylesheet" type="text/css" />
<!-- /YUI Styles -->
<link href="../../Content/knowledgebase.css" rel="stylesheet" type="text/css" />

<script type="text/javascript">
    //this hides the javascript warning if javascript is enabled
    (function($) {
        $(document).ready(function() {
            $('#jswarning').hide();
        });
    })(jQuery);
</script>

<asp:ContentPlaceHolder ID="ScriptContent" runat="server" />

<script src="<%= Url.Content("~/Scripts/jquery-1.2.6.js")%>" type="text/javascript"></script>

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.2.6/jquery.min.js"></script>

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js" ></script>

<script src="<%= Url.Content("~/Scripts/jquery-1.2.6.js")%>" type="text/javascript"></script>

<script src="<%= ResolveUrl("~/Scripts/jquery-1.2.6.js")%>" type="text/javascript"></script>