This error message occurs when exporting to AFAS if it was not possible to add an attachment to the sales booking.
Are you working with AFAS Small Business?
In AFAS Small Business it is not possible to send booking documents for sales bookings.
Solution: remove the 'Sales dossier item type' in the administration settings. Go to Manage / Environment / Administrations, click 'Edit' and go to the tab 'AFAS'. When the number in 'Sales dossier item type' is removed, bookings can still be exported without an attachment. The booking document and attachments will of course remain available in the Zenvoices archive.
Are you working with AFAS Profit?
Consult the information in this article for more information.