Outlook 2007 Cannot send mail. NDR goes to incorrect mailbox.

I have an Exchange mailbox in Outlook 2007 that is completely unable to send outbound messages.  Cannot send to local recipients, outside, or self.  The mailbox CAN download, open, and read all messages.

When a new message is sent from this Outlook client, the message is immediately rejected by the server and the error message is delivered to a DIFFERENT mailbox:
You do not have permission to send to this recipient.  For assistance, contact your system administrator.
The sender does not see any failure message at all, and the person receiving the NDR is thoroughly confused as to what the error messages are.

The mailbox IS accessible via OWA and can successfully for send and receive.  The mailbox in question CAN be successfully added to another Outlook client on another computer AND can send and receive messages from this other computer.

What I've tried:
1. Completely removed Outlook profiles from local computer and restored them from the server. 
2. Completely uninstalled Office 2007 and reinstalled entire Office system from original source.
3. Verified permissions on Exchange Server (2003) for the account.

What else can I try??  I am stumped!

-Jacob