Work item &: Agents of type & cannot be deleted

What causes this issue?

The agents of the specified type could not be deleted 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 applicable, enter
the correct agents.
INCLUDE NA_WF-ADMINISTRATOR OBJECT DOKU ID TX
Please also note the long texts for the error messages
<DS:NA.WL840>WL840</> and <DS:NA.WL841>WL841</>.

Error message extract from SAP system. Copyright SAP SE.