Well the error looks like a MAPI issue, this usually comes in SMBR 6.0 in case you aren't using Outlook on the SMBR server.
In your setup, have you installed SMBR on the Exchange server directly ? If yes, then make sure you have Outlook 2007 SP2 installed on the SMBR server as well.
In case no, then also make sure your Outlook version is as per the minimum requirement specified on the Product Doc.
PS : SMBR uses Outlook MAPI services to connect to the Target Exchange server Mailboxes.