Just completed an SBS 2011 migration from SBS 2003 using the Microsoft method. Two of the mailboxes failed to transfer correctly and I had to manually create and import them. Subsequently some staff were unable to email one of those mail accounts.
They received an undeliverable error which showed the new server name but trying to route to the old 'First Administrative Group' on the 2003 server. Download Offline Address Book gave error 0x8004010F, not found.
Creating a new OAB in 2010 Exchange Management Console didn't appear to fix the problem. Found the key bit of info here
Create the new OAB with a different name. Then allocate it to the Mailbox Database. Going back to Outlook and clicking Download Address Book worked straight off and email routing was successful.