This error occurs when the value of the FathId in table OUPT is null instead of an empty string.
When the add-on add it's own row, then it adds empty string. So this can be fixed by triggering the add-on to re-create the entry.
Please follow the steps below when nobody works/logged in SAP:
1. Create a Database backup in case you will have to restore
2. Login SAP
3. Stop WMS add-on if it starts automatically
4. Open "Additional Authorization Creator" window.
5. Delete the whole PMX_PR tree (You will have to press Update button at the bottom of the window)
6. Start the WMS add-on.
The authorizations will be generated during the starting phase.