If the separate sales tax parameter is enabled in AR module, the client is not able to write off the credit note. They are getting the error message "The write off process is complete. The separate sales tax check box is selected in the accounts receivable parameter form. You must settle all credit transactions before you write off transactions."

The credit note should write off without any error message even when the separate sales tax parameter is enabled.

In France, credit note is also created for other purposes like additional payment which is booked as profit at year end if it is not claimed by customer. Hence, it cannot be settled with any invoice. Also, at times, conditional taxation is also configured and therefore while doing write-off of credit note, separate sales tax line is needed.