the code for the add to cart button form action is not correct.
change:
<form name="Nitrodog_1_ATC_90088" method="POST" action="<?php echo $_SERVER["file:///C|/Users/L. Ofiana/Adobe Dreamweaver CS5.5/ecart/PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>">
to:
<form name="Nitrodog_1_ATC_90088" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>">