After removing Exchange 2010 and trying to reinstall you get error Database is mandatory on UserMailbox. Property Name: Database

Here is the error:
Summary: 5 item(s). 1 succeeded, 1 failed.
Elapsed time: 00:00:09
Preparing Setup
Completed
Elapsed Time: 00:00:06
Hub Transport Role
Failed
Error:
The following error was generated when “$error.Clear(); if ( ($server -eq $null) -and ($RoleIsDatacenter -ne $true) ) { Update-RmsSharedIdentity -ServerName $RoleNetBIOSName }” was run: “Database is mandatory on UserMailbox. Property Name: Database”.
Database is mandatory on UserMailbox. Property Name: Database
Elapsed Time: 00:00:03
Client Access Role
Cancelled
Mailbox Role
Cancelled
Finalizing Setup
Cancelled
In order to fix this it is actually pretty simple
1.  Go to start>run>adsiedit.msc
2.  Open default naming context
3.  Open your domain user OU should be labeled CN=users
4.  Find the account that starts with CN=federated
5.  Right click on this and delete the object
6.  Run setup.com /prepareAD
7.  Run setup.com /prepareSchema
8.  Once you do this re-run setup and it will succeed