Activity is already dispatched. You cannot change dates.

What causes this issue?

The activity has already been dispatched in capacity planning. In this
situation, you can no longer change the dates for the activities.

System Response

INCLUDE 'NA_ALLG_NOFUNKTION' OBJECT DOKU ID TX

How to fix this error?

To change the activity dates, you must first deallocate the activity
in capacity planning.

Error message extract from SAP system. Copyright SAP SE.