that code should go at line 1 of the cart page.
also on the cart page page, change:
<form action="<?php echo ($_SERVER["PHP_SELF"].(isset($_SERVER["QUERY_STRING"])?"?".htmlentities($_SERVER["QUERY_STRING"]):""));?>" method="post" >
to:
<form action="<?php echo $_SERVER["PHP_SELF"]; ?>" method="post" >