Cause
- You are trying to print one or more invoices from transactions table that do not belong to a customer group.
Solutions
- To print invoices, the registrations must contain an account (or a cost center) that belongs to the customer group. As a result, check the columns Debit, Credit and/or CC3.
- Check the customer group settings in the Report > Customers > Settings.
See also setting up the customer account and configuring the Customer settings.