your form uses the post method:
<form name="form1" method="post" action="under2.php?id=$rsCourses.csrID" >
and the name for the courses select list is "Courses":
select name="Courses" size="1" class="boxLen" id="Courses">
so in the recordset, the run time value for the colname variable should be:
$_POST['Courses']