Solution : https://service.sap.com/sap/support/notes/847243 (SAP Service marketplace login required)
Key words :
message ff810 appears, exchange rate difference, tax rate exists, ro/enjoy symptom, tax exchange rate, local currency amount, exchange rate, tax amount, local currency, tax screen
Related Notes :
851932 | FF747 with manual change to tax amount in local currency |
797370 | MIRO MR8M - Alternative tax base value is not posted |
719340 | MIRO FB60 FB70 - tax base cannot be changed |