in your form, you have a hidden form element:
<input name="WADAInsertRecordID" type="hidden" id="WADAInsertRecordID" value="" />
find that element and edit it to:
<input name="WADAInsertRecordID" type="hidden" id="WADAInsertRecordID" value="<?php echo(isset($_GET['Inventory_ID'])?$_GET['Inventory_ID']:""); ?>" />