I replaced a DC running Exchange 2003 with a new server running Server 2008 r2 running Exchange 2007. Everything is working fine, however when they download the OAB they get the error 'Microsoft Exchange' reported error (0x8004010F) : 'The operation failed. An object cannot be found.' and when new users are added they don't show up in the Gal.
I installed exchange sp3, rebuilt the oab, and replaced the gal with a new address list.