Dan Martin wrote:
When installing, I enabled / selected kerberos and LDAP, thinking I might want them in the future - I did not configure them. Do I have to reinstall without them?
Yup, that's your problem all right... the PAM authentication subsystem is attempting to contact the kerberos and/or ldap servers at every login, but has nowhere to go and so returns failure.
As root, simply run "setup" from a terminal and choose "Authentication setup", and deselect anything you're not actually using right now.
-Adam