all the code looks correct, the only thing i can think, is that you have renamed the page, but not changed the forms action:
<form action="productcategories_Insert.php" method="post" name="WADAInsertForm" id="WADAInsertForm">
the forms action is set to post to the productcategories_Insert.php:
if you created a back upo pf that file and are adding the modifications to the back up, you would be bypassing them.
try changing the form tag to:
<form action="" method="post" name="WADAInsertForm" id="WADAInsertForm">
if you continue to have problems, please compress the original php page to a zip archive and attach the zip file to your reply rather paste the page code.