In your Login keychain, delete the certificate.Delete any keychains on the left that resemble OC_Ke圜ontainer_.In the Applications/Utilities folder, open Keychain Access. If you delete the Microsoft Lync History folder, you delete all conversations that are saved in the Conversation History. To remove all Lync files from your computer, delete the following folders in the Users/username/Documents/Microsoft User Data folder: Users/username/Library/Logs/Microsoft-Lync.log Note This file is present only if you turned on Lync Logging. Users/username/Library/Logs/Microsoft-Lync-x.log Users/username/Library/Preferences/ByHost/ To remove your existing Lync preferences, delete the following files: Log on to your computer by using administrative credentials. If the issue is resolved by creating the new profile, it will be determined that the issue was caused by a corrupted profile. If you contact Microsoft technical support, you may be asked to create the new profile as a troubleshooting step. You may be able to avoid uninstalling Lync for Mac 2011 if you create a new profile on the Mac.