General task list is already being processed

What causes this issue?

You selected a general maintenance task list which is being edited
either by you in another mode or by another user.

System Response

The system locks any further editing calls until the editing that is
currently active has been completed.

How to fix this error?

Check whether you called up the task list yourself in another mode. If
so, continue processing it there.
If another user is editing the task list, wair till that person has
finished.

Error message extract from SAP system. Copyright SAP SE.