Diagnosis
The withholding tax term and posting term you assigned have differentbusiness partners.

System Response
This assignment is not possible. When the condition is posted, thesystem checks the withholding tax term against the withholding tax datain the master data of the partner of the condition (posting term). Thischeck makes sense only if both terms have the same partner.

Procedure
If applicable, create a withholding tax term that has the same partneras the posting term, and assign this term to the condition.