Thought I doc'd this but can't find it.
In some cases you may find that you can no longer log into the console of a system, but can still access it via SSH.
I've had this happen a couple of times after a consultant tried installing Oracle without correctly identifying the "bitness" of the host.
Checking /var/log/secure while trying to access the console, you might find:
Sep 20 04:14:28 someuser login: PAM adding faulty module: /lib/security/pam_limits.so
If your system is 64bit, the problem in this case can be that someone has linked in a 32bit library for PAM.
You'll probably find /etc/pam.d/login points to /lib/security/pam_limits.so rather than /lib64/security/pam_limits.so.
Just relink them correctly and the console login should start working again.