Sometimes the contact list may be corrupted (example: invalid character in an “out of office” message), so it happens that you cannot search for contacts within Lync 2010 and a restart of the application, the whole PC system etc. don’t help out either.
So what can you do?
Firstly close Lync and Outlook!
Then delete the following local user centric Lync 2010 databases and caches within the folder %localappdata%\Microsoft\Communicator\sip_<sign-in name=””></sign-in>
- ABS_<sign-in name=””></sign-in>.Cache
Usually it takes a random time after Lync 2010 starts to sync the address book, so add this registry entry and it will start syncing immediately:
reg add HKLM\Software\Policies\Microsoft\Communicator /v GalDownloadInitialDelay /t REG_DWORD /d 0 /f
Start Lync 2010 now and you should be able to search for contacts nearly immediately.
You can find some more insights about “Updating the Lync 2010 Address Book” here.