Exchange 2010 System Attendant errors/warning after removing default database

When an Exchange 2010 mailbox server is installed it automatically recreates a default database. After you've created your own databases it makes sense to delete the default one. If you research this you'll see you need to move the hidden arbitration mailbox from the default database to another one, and then you can delete it. However, after deleting it you may start getting System Attendant errors or warnings in the event log. It is caused by the HomeMDB attribute of the System Attendant object no longer being valid, even though the System Attendant doesn't actually reside in any database.

Sometimes just restarting the System Attendant service with fix the issue as it will put a valid database path into the HomeMDB field. However, sometimes it doesn't. To fix it manually you need to open ADSIedit and drill down to Configuration > Services > Microsoft Exchange > [your site] > Administrative Groups > [your Exchange 2010 administrative group] > Databases. Select one your databases, view its properties, and copy the value for distinguishedName. Now expand Servers, expand your mailbox server(s), and select the properties for Microsoft System Attendant. Past the distinguishedName value into the HomeMDB attribute. Repeat for any other mailbox servers, and then restart the System Attendant service on the affected servers.