I had the same problem. It's most likely you left something out of your admin/categories.php file. Do you have this line in it's entirety;
$sql_shipping_array = array('products_ship_zip' => tep_db_prepare_input($_POST['products_ship_zip']),'products_ship_methods_id' => tep_db_prepare_input($_POST['products_ship_methods_id']),'products_ship_price' => round(tep_db_prepare_input($_POST['products_ship_price']),4),'products_ship_price_two' => round(tep_db_prepare_input($_POST['products_ship_price_two']),4));//psm
Mine is around line 289. Hope this helps.