I have a similar problem like another user had and followed all possible steps including reinstalling and cleaning up Keychain etc before.
The first time I start Lync after a reinstall, I can even see a Menu bar for some seconds. But before any window gets rendered, the Crash Reporter opens.
This is what the error said:
Microsoft Error Reporting log version: 2.0
Error Signature: Exception: EXC_BAD_ACCESS Date/Time: 2013-10-30 13:23:14 +0000 Application Name: Microsoft Lync Application Bundle ID: com.microsoft.Lync Application Signature: UCCP Application Version: 126.96.36.199930 Crashed Module Name: libcorecrypto.dylib Crashed Module Version: unknown Crashed Module Offset: 0x0002783a Blame Module Name: Microsoft Lync Blame Module Version: 188.8.131.52930 Blame Module Offset: 0x002cc862 Application LCID: 1031 Extra app info: Reg=English Loc=0x0407 Crashed thread: 0
Any Ideas how to solve this?