Diagnosis
You attempted to write the time type that is currently being processedto the Previous period's period balance and Period balanceprev. year fields. However, these fields are used to transfer aperiod balance at the end of a period to another period balance.

Procedure
If you want to transfer the period balance manually to a subsequentperiod, set the Transfer from previous period or Transferfrom previous year indicator.
If you want to transfer the period balance to another balances, enterin the relevant fields a time type other than the time type that iscurrently being processed.