If you receive this error:

The Lync 2010 client or the Office Communicator client does not download the corporate address book and displays a notification: "Cannot Synchronize Address Book"

Give the following a shot:

1. Shutdown the Lync client
2. Force the Lync client to download the address book immediately the next time it starts:
   • Open the registry to HKLM\Software\Policies\Microsoft\Communicator
   • Modify (or Create) the DWORD  the registry key “GalDownloadInitialDelay” and set it to 0  (that is a zero)
   • This can also be done from the command line:
     • reg add HKLM\Software\Policies\Microsoft\Communicator /v GalDownloadInitialDelay /t REG_DWORD /d 0 /f
3. Delete the Existing Local Address Book Files:
   • On Windows 7 or Vista machines, open Windows Explorer to the directory:
     • %userprofile%\AppData\Local\Microsoft\Communicator\sip_user@example_domain
   • Delete the files GalContacts.db and GalContacts.db.idx
4. Restart the Lync client.
   •    The address book should be available in less than an hour.

I found the solution here: http://blog.insidelync.com/2012/02/lync-address-book-client-synchronization-errors-and-common-problems/  Give it a read, it's very thorough.