1. On the Lync 2010 Server launch the “Lync Server Management Shell” and execute the following command:
2. Go and have a cup of coffee, then come back and check in the event logs, you should see, Event 21005 (Sync has Started), 21010 (Sync has completed), 21056 (Details of the sync), and 21004 (Time of next sync).
3. If that does not rectify the problem you can run the following command with administrative privileges:
reg add HKLM\Software\Policies\Microsoft\Communicator /v GalDownloadInitialDelay /t REG_DWORD /d 0 /f
Create or edit a the DWORD GalDownloadInitialDelay and set its value to 0.
4. Close the Lync Client and delete the GalContacts.db and GalContacts.db.idx files form that PC. you will find those file in the following locations
Windows 7,8 : %userprofile%\AppData\Local\Microsoft\Communicator\sip_<the_username@the_domain>\
4. Restart Lync Client. That’s it.