Provisioning Server manages the objects over Lotus Domino, but there is also another custom system who works on the same objects.
To prevents collisions the Lotus engineer decides to set the "Allow document locking" flag ON for their Public Address Book (PAB).
Trying to delete any groups as "<AddressBook.nsf>:<MyGroup>" fails with:
Failed to find doc using formula 'ListName = "<MyGroup>"' in <AddressBook.nsf>, due to: NotesException: Notes error: Document locking is enabled.
You must lock the document before deleting.
Currently, By design, there is no way to perform this action from IM.
So, you can lock the group document from IBM Domino Administrator UI.
This can be done from the Actions tab by clicking on the "Lock Document" action once you have selected the group.