Save Bill > Error: Invalid taxcode reference key XX for subsidiary X. Tax code used on the Bill is YY. However, the tax code referenced above is XX.
Check if the vendor on the bill has an assigned tax code. You can confirm this by clicking the Subsidiaries tab.
Check if the tax code is only available for Sales Transactions. If yes, this is the reason why you cannot save the bill since bill is a Purchase Transaction.
1. Remove the tax code on the vendor record; or
2. Make the tax code available for both purchases and sales transactions.