It looks like you also have your weight column bound to a field: "eCart1_1_Weight_Add" which doesn't exist. You probably want to get that from your database instead.
The second error is as a result of this one.
If you want to get the quantity from the input field on the page, you would want to name it uniquely for each row so that it can be identified like:
name="quantity_<?php echo $row_ProdSizeSelectList['ID']?>"
and then you could bind it to that value by updating line 153 to:
$ATC_itemQuantity = "".$_POST["quantity_".$row_WADAProd['ID']] ."";// column binding