on the acclients_insert.php page, the form action does not pass the URL
<form class="Basic_Default" id="Insert_Basic_Default" name="Insert_Basic_Default" method="post" action="<?php echo (htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)); ?>">
change that to:
<form class="Basic_Default" id="Insert_Basic_Default" name="Insert_Basic_Default" method="post" action="<?php echo (htmlentities($_SERVER["PHP_SELF"], ENT_QUOTES)); ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".htmlspecialchars($_SERVER["QUERY_STRING"]):""; ?>">