Thanks Jason, but that still doesn't work. This is what I have:
<form action="<?php echo htmlentities($_SERVER["PHP_SELF"]); ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".htmlentities($_SERVER["QUERY_STRING"]):""; ?>" method="post" name="WAATKLogInForm" id="WAATKLogInForm">