Invoking the "Assign" method in a custom script with the intention to change a PersonWantsOrg object's orderstate property to "Assigned" results in the following error:
 Error executing script 'XXXXXXX'.
 Method Assign(VI.DB.Entities.ISession, VI.DB.Entities.IEntity, System.String, System.String, System.Threading.CancellationToken) is been deactivated and cannot be called.
In general, whether customizer methods are enabled or not can depend on object states.
In this particular instance, the PersonWantsOrg object's orderstate property is "Unsubscribed" or "Aborted". In order to prevent silently re-granting permissions, an orderstate change from these states to "Assigned" is not allowed, hence the method "Assign" is also deactivated.
Check the orderstate before invoking the method "Assign".