[ERROR] Database is mandatory on UserMailbox. Property Name: Database

When you try to apply SP1 or SP2 on Exchange 2010 Server, you may receive the error stating that “Database is mandatory on UserMailbox. Property Name: Database.” in the Exchange setup log.

This error is caused by some information that missed in “System Mailbox”. In our case, “System mailbox” aren’t affected to a specific database. There are two solutions:

First Workaround:

1- Delete system mailbox from Active Directory using ADSI tools

• Click Start, click Run, type adsiedit.msc, and then click OK.
• Locate the Default Naming Context node, and then locate to the CN=Users container.

Locate:

• "DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}"
• “System mailbox”
• Delete them

2- Run Setup.com /prepareAD, then, System mailboxes will be created

3- SP2 installation will be finish succesfully

Second Workaround:

1- Locate system mailboxes in AD with ADSI

2- Change HomeDB parameter, and affect mailboxes to an existing database

3- Rerun SP2 setup, it will finish succesfully