1. Set the Lync client initial delay for address book download to 0: Start the registry editor, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Communicator, and create a new DWORD value named GalDownloadInitialDelay, then set the data to 0 and click OK.
2. Close the Lync client if it’s running and delete the GalContacts.db and GalContacts.db.idx files, which you will find in your profile (e.g., C:\Users\john117\AppData\Local\Microsoft\Communicator\firstname.lastname@example.org folder).
3. Start the Lync client, and the address book should download.