Tax amount different to expense/revenue account assignment - correct

Question

Hi All,
While posting a vendor invoice we are getting error message "Tax amount different to expense/revenue account assignment - correct".
Message no. FF796
Diagnosis
You have entered a manual tax amount in the first vendor or customer line.
This tax amount has a different debit/credit indicator to the expense or revenue items relevant for tax that you entered. The tax would therefore be displayed as negative.
The tax entry for the vendor or customer items is posted internally with the reverse debit/credit indicator to that of the vendor customer item itself.
System Response
The system does not permit the posting of the document in this way.
Procedure
Delete the tax amounts and tax codes from the vendor or customer item and enter the tax data on the tax screen.
In the Enjoy transaction FB60/FB0, you can use the function "Propose Net" to determine the correct debit/credit for tax from the expense items.
Can anyone please tell what settings are causing this error and

Answer 1

The requirement is simple now and hope I may get some answes .
My issue is the Sales order on free sample we want to charge the expense account insteadof  Customer account  and is happening . We are not clear from where the Exp Gl account is picked .
The TAX Gl accounts in OB40 or VKOA configuration does not show  the exp GL account( which is substituted instaed of Customer invoice during billing.)
It is not clear from where the GL account is flowing, We are using taxware. Before approaching Taxware thought to get opinion  from experts,
Regards,