Hi,
You have that error because you have setup Prepayment Invoices in the Sales Order. The error that you get, it can be for two reason:
- Prepayment Invoice is not Posted;
- Prepayment Invoice is still remaining of payment.
When you use Prepayment in a Sales Order and the field Check Prepmt. When Posting = Yes in Sales & Receivables Setup., the system will validate if your client has payed the Prepayment Invoice, with that, you guarantee that your items are not shipped to the customer until a prepayment has made.


To resolve your problem please check one of these options:
- Please check If you post the Prepayment Invoice, in the follow Button:

If you do not have any Prepayment Invoice Posted, you need to click on the follow Button and then you need to do the steps indicates on the point 2) bellow:

2. If you already post the Prepayment Invoice, you need to post the Payment received from your customer and applied to the respective Prepayment Invoice that you post from the Sales Order. Only when your Prepayment Invoice is totally paid, you can proceed with the Sales Order Post (Ship and Invoice).
Note: In case you do not want this validation, you can disable the field, “Check Prepmt. When Posting” in Sales & Receivables Setup.
Hope It help. If you have any questions, please let me know.