Actual finish date for WBS element & cannot be maintained

What causes this issue?

You cannot enter any actual finish dates for WBS element &V1& if
the subordinate WBS element does not have an actual finish date
or the activities in the WBS element do not all have final confirmations

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Enter the actual dates for the subordinate WBS elements.

Error message extract from SAP system. Copyright SAP SE.