Start Date should be less than End Date validation in jQuery DatePicker in ASP.Net

Dear All, I am using the DatePicker - Start Date and End Date from the article: https://www.aspsnippets.com/Articles/jQuery-DatePicker-Start-Date-should-be-less-than-End-date-validation.aspx

The article works well after testing.

I have the following set in ASP.Net web page:

<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js" type="text/javascript"></script>
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css" rel="Stylesheet"type="text/css"/>

<script type="text/javascript">
    $(function () {
        $("#txtCourseStartDato").datepicker({
            numberOfMonths: 2,
            onSelect: function (selected) {
                var dt = new Date(selected);
                dt.setDate(dt.getDate() + 1);
                $("#txtCourseSluttDato").datepicker("option", "minDate", dt);
            }
        });
        $("#txtCourseSluttDato").datepicker({
            numberOfMonths: 2,
            onSelect: function (selected) {
                var dt = new Date(selected);
                dt.setDate(dt.getDate() - 1);
                $("#txtCourseStartDato").datepicker("option", "maxDate", dt);
            }
        });
    });
</script>    
                
  
<tr>
    <td>&nbsp;</td>
    <td>
        <asp:TextBox ID="txtCourseStartDato" runat="server" BackColor="#ffffff"  type="text" Width="135px"></asp:TextBox>
        <asp:TextBox ID="txtCourseSluttDato" runat="server" BackColor="#ffffff"  type="text" Width="135px"></asp:TextBox>
    </td>
    <td></td>
</tr>

This code is not firing on my page. What could be the issue?

Many thanks