Either select only one WBS element or no WBS element

What causes this issue?

The finish date that you entered for the activity is later than the
finish date in the superior WBS element.

System Response

INCLUDE 'NA_ALLG_VERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

If you use top-down planning, the activity dates should lie within the
time frame of the superior WBS element.
The system checks the dates when you save. If there is a scheduling
conflict, you must adjust the dates accordingly.

Error message extract from SAP system. Copyright SAP SE.