Can't sign in with MS Lync
Solved this today. I'm not sure what finally solved it but this is what I did ...


Install the latest Mountain Lion Update which was published today
Completely uninstall Lync as described here http://support.microsoft.com/kb/2691870 
Reinstall Lync + do the Lync update to v14.0.6
Change my password - as my old one contained a German special character.