Hello , im trying to send cancelled invoices to credit memo table with all the line items.  What im trying to do is duplicate line items with negative  values (negative values is to keep real inventory) but my loop is not working , it only duplicates the first row. 

Please let me know how do you deal with this ? 

Well, in my solution, the credit memos and invoices are in the same table, just with negative quantities.

Anyway, post your script. You're obviously not looping thru the line items correctly. You could also import from one table to the other. (If you keep the extra tables).