Work item &: Agents of type & cannot be written

What causes this issue?

The agents of the specified type could not be written for the specified
work item.
INCLUDE WF_BEARBEITERTYPEN OBJECT DOKU ID TX

System Response

The action was terminated.

How to fix this error?

Search for the work item via work item selection.
If necessary, enter the correct agents.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

INCLUDE NA_WF-ADMINISTRATOR OBJECT DOKU ID TX
Please also refer to the long text for error message <DS:NA.WL840>WL840
</>.
Please note for a correction that changes in the organizational model
do not have any additional effects on the evaluation of a rule for
agent determination, as it is only evaluated when the work item is
created.
However, changes to the organizational assignment of the task become
effective immediately since they are re-evaluated when the Business
Workplace worklist is compiled.

Error message extract from SAP system. Copyright SAP SE.