The recent update to Mac OS X 10.7.2 installs an invalid login certificate. Lync for Mac crashes because of this invalid login certificate.
Solution: Delete this login certificate.
1. In Finder, go to /Applications/Utilities, and open Keychain Access
2. On the left navigation pane, under Keychains, click login
3. On the left navigation pane, under Category, click Certificates
4. Find the certificate Unknown and delete it
5. Restart Lync for Mac