Maintain the rates either in CO area currency or object currency

What causes this issue?

You can maintain the rates either manually in the company code currency
or in the object currency, but not both at the same time.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

If you want to use the planning parameters in a controlling area without
foreign currencies (flag: "All currencies.. X" in the customizing of
the controlling area), or without cost centers with the currency
differing from the company code currency, select manual maintenance of
the rates in company code currency.
Only select manual maintenance of the rates in object currency if you
want to use the planning parameters with cost centers whose currency
differs from the company code currency.

Error message extract from SAP system. Copyright SAP SE.