I also ran into this after a partial upgrade of a 14.04 system today. I've seen this before on a different machine after upgrading to 13.10, but in that case 'sudo pam-auth-update --force' fixed the problem. This time that doesn't help.
I also ran into this after a partial upgrade of a 14.04 system today. I've seen this before on a different machine after upgrading to 13.10, but in that case 'sudo pam-auth-update --force' fixed the problem. This time that doesn't help.