Actual data and reference data must both be posting or special periods

What causes this issue?

If the option "Cumulate periods" has not been selected, then the
periods for actual data and reference data both have to be posting
periods or they both have to be special periods.

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?

Enter either posting periods or special periods, but not both.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.