This update is required if the Offline Address Book (OAB) generation is moved from an Exchange 2007 server to an Exchange Server 2003 Service Pack 2 (SP2) server. It resolves issues which are caused due to changes in the OAB version 4 in Exchange 2007.
This update is also recommended if the OAB is generated on an Exchange Server 2003 SP2 server after Exchange 2007 is deployed in the Exchange organization.
Download update: http://www.microsoft.com/downloads/details.aspx?amp;amp;displaylang=en&familyid=B217A4C9-4AAD-49B9-92DD-10754AF1029E&displaylang=en
Error message when you try to change the offline address list server from Exchange Server 2007 to Exchange Server 2003: "The target server cannot support OAB"
http://support.microsoft.com/?kbid=922817