passwd/shadow inconsistencies

If your system issues messages of this type:

su: Authentication failure
(Ignored)

Authentication service cannot retrieve authentication info

Also in /var/log/syslog:

CRON[12591]: Authentication failure

and su and sudo continue working but cron fails, probably you have a /etc/passwd inconsistency respect to /etc/shadow.

Just execute:

$ pwconv
$ grpconv

..to fix them.