Hi
Are you using New GL or classical GL?
How is Business area derived in other transactions that you mentioned it is working successfully and do they also use the same substitution rule through Exit? If yes, what is the functional logic for deriving business area. As a standard, Business area will not get updated generally on tax line items in classical GL and one needs to perform a business area classification. If you could give some background on the same, it will help. I assume you are talking of the tax payable account, which is a balance sheet account and you are not bearing the tax liability in your books through an accrual.
Regards
Sanil Bhandari