When decommissioning an Exchange server 2007 following a migration to Exchange 2013 is likely that you will see this message:
The error is clear, you can not uninstall an Exchange server that is responsible for the generation and distribution of an offline address book, then first check that all of the new 2013 infrastructure DB are set to the new offline address book 2013 server generated (You can check it the database properties -> client settings).
Second thing: OAB is not to be migrated as happened for example during the migration to Exchange 2010, in this case, yet during the installation of 2013, a new OAB is created with the same name as the existing one with a “(Ex2013)” as a suffix then we just have to remove the old OAB managed by 2007; to do this just open the EMC and go to EMC -> Organization configuration -> mailbox -> TAB Offline Address Book, Right click on the 2007 Offline address book -> remove (or delete).