the redirect querystring is getting the ID from the rsOrders recordset
$WA_redirectURL = "orders_Detail.php?OrderID=".$row_rsOrders['OrderID'] ."";
the rsOrders needs a OrderID querysting to be passed into it to filter correctly, but the forms action does not pass this in:
<form action="inventory_Update.php?InvID=<?php echo(rawurlencode($row_WADAinventory['InvID'])); ?>" method="post" name="WADAUpdateForm" id="WADAUpdateForm">
change the form tag to:
<form action="inventory_Update.php?InvID=<?php echo(rawurlencode($row_WADAinventory['InvID'])); ?>&OrderID=<?php echo(rawurlencode($row_rsOrders['OrderID'])); ?>" method="post" name="WADAUpdateForm" id="WADAUpdateForm">