A difficult task

[odrap]

In a form with two listboxes, one is meant to display the orderID's of all orders that may be invoiced and the second to gather the orderID's selected in the first listbox.
Each orderitem , as part of an order, has a field "INV" of type True/False, to mark the fact that this orderitem , although part of the selected order to be invoiced, for the moment may or may not be invoiced ,thus must be excluded or not.
When an orderitem in the first lisbox is selected who has orderitems that are marked as to be excluded for invoicing, i like to see a message or something else, informing the user that the order ,he or she selected for invoicing, contains one or more orderitems that may not be invoiced for the moment and therefore must be excluded of the set of orderitems from this order to be invoiced. Because an order contains most of the cases more then one orderitem,all the orderitems , as part of the selected order has to be examinded to determine if at least one orderitem is marked as such. As soon as such an orderitem is detected, the such may stop and the message must popup.
PS. The field "inv" is a field in the table "tblOrderdetails", while the orderid's shown in the first listbox comes from the table "tblOrder".

 

[jzwp22]

Why don't you filter the first list box to only include those invoices that can be invoiced (i.e. all items are marked as invoiceable); it would be less confusing to your users. Also, I would just use 1 list box--a multiselect list box. That way your user can highlight the ones they want to invoice and then move on from there.