Need help deleting account in Exchange 2010

I had a SBS swing migration (2003 to 2011) about a year ago that more or less went pretty well. All of the mailboxes moved from the old server (KCFDDC) to the new server (D20DC) except for one. This mailbox is attached to an admin account that I don't want to delete. I just want the mailbox to either work in Exchange 2010 or delete the mailbox and create it again (I need this mailbox to work coming up).

In the Exchange 2010 Console it shows this mailbox as a legacy mailbox (the only one in the whole organization). When I choose "properties" I get a warning that "the properties in this object contain invalid data....." I can't disable this mailbox. I can't perform a move request or any sort. And I can't perform a "disable-mailbox" command from the Exchange Shell. I get this result:

 The property can't be empty.
    + CategoryInfo          : NotSpecified: (0:Int32) [Disable-Mailbox], DataValidationException
    + FullyQualifiedErrorId : 29B5D572,Microsoft.Exchange.Management.RecipientTasks.DisableMailbox
    + PSComputerName        : d20dc.acme.local
 

My end goal is to have a functional admin level mailbox for this account that I can use for various admin related Exchange functions.

Please help!! Thanks!