http://blogs.technet.com/jitreddy/archive/2008/08/07/unable-to-download-address-book-from-office-communicator-2007-prompting-for-credentials.aspxAfter installing OCS, you find that you're not able to download the Address Book. Office Communicator will prompt for the entry of credentials over and over while trying to download the address book but credentials will not be accepted. You'll see theen-USCommunityServer 2.1 SP1 (Build: 61025.2)