Mailbox server role issue installing SP2

Hi all,

I wish you an Happy New Year 2012 !

I'm trying to install SP2 for Exchange 2010, and during the step about the mailbox role, this error occurs :

Mailbox Server role
Failure

Error :
Following error occured during execution of "$error.Clear();
if ($RoleCreatePublicFolderDatabase)
{
$publicDB = get-PublicFolderDatabase -Server:$RoleFqdnOrName -ErrorAction SilentlyContinue;
$DB = get-MailboxDatabase -Server:$RoleFqdnOrName -ErrorAction SilentlyContinue;
if ($publicDB -and $DB)
{
set-mailboxdatabase `
-Identity:$DB.Identity `
-publicFolderDatabase:$publicDB.Identity `
-DomainController $RoleDomainController
}
}
" : "Can't bind argument to parameter « Identity », because its value is Null.".

Can't bind argument to parameter « Identity », because its value is Null.

Time elapsed : 00:05:35

End of installation.

Canceled

I can't find anything about this error. But it's surprising, the Exchange server seems running perfectly, and 2 new mailbox databases were created automatically, and they are unmounted.... Je ne trouve rien concernant cette erreur.

Thank you. have a good day.