You can disable or remove an arbitration mailbox that is used by Offline Address Book (OAB) by running the Disable-Mailbox or Remove-Mailbox cmdlet in a Microsoft Exchange Server 2013 environment.
You expect that the command fails if the arbitration mailbox is used by OAB.
To resolve this issue, install the following cumulative update:
2961810 Cumulative Update 6 for Exchange Server 2013
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.