Diagnosis
There is a time gap between the newly assigned account settlementvariant and the next account settlement variant where no accountsettlement variant is assigned to the calculation unit.

System Response
The entry is refused.

Procedure
This problem can only occur if the newly assigned account settlementvariant is year-dependent, i.e. is only valid for an account settlementyear. You either have to change or delete the subsequent accountsettlement variant which you entered and/or assign another accountsettlement variant.