can't login as user

[DrChuck]

Hi all,
Ive been running FC3 on an older sandbox machine for about a month with no problems. Today I reboot, and can't log in graphically with my user account: I get a popup claiming "Authentication failed". I checked /var/log/messages:
[date] [hostname] gdm[3163]: Couldn't set acct. mgmt for [username]
From a virtual console, I attempt to login. The following message flashes, before I get the login prompt back: "authentication service can not retrieve authentication info". If I intentionally use an incorrect password, I get a different message "Login incorrect", and a "failed login" in the messages log. It appears that I am partially authenticated with the correct password, but not logged in?
I can login as root with no problems. I tried to reset the password for my user account, and it was accepted, but I still can't login. I created a new user account, and can't login to that one either.
Somethin is quite hosed. I haven't done anything I would consider risky as root, mostly running up2date. I would prefer to reinstall the packages related to the login process, and not do a full reload, but I'm not sure which packages are relevant. Here is some of the authentication stuff which is installed:
pam_passwdqc-0.7.5-2
pam_smb-1.1.7-5
pam_krb5-2.1.2-1
pam_ccreds-1-3
pam-0.77-66.1
krb5-workstation-1.3.6-2
pam_krb5-2.1.2-1
krb5-auth-dialog-0.2-1
krb5-libs-1.3.6-2
Any ideas on how I can recover from this?
Thanks for reading,

[KarrottoP]

is it possible that you have come dangerously close to filling your hard drive to capacity. I found that that will allow root only acess.

[DrChuck]

Thanks for the reply. In the past I've run into the exact situation you describe, but currently I'm at only 68% on the root partition.

[KarrottoP]

Is it possible that you have permissions set incorrectly on the users home directory and can not get to the bash profile?

[DrChuck]

Permissions all look ok, but thanks KarrottoP for the suggestion.
I don't know what suddenly changed to break my system, but I managed to "fix" it by running authconfig (RedHat-only tool?) as root . I turned off kerberos, and left MD5 passwords and shadow passwords and SMB authentication on. I'm not even sure how kerberos works, because all the settings in the krb config files were default values, like ".example.com = EXAMPLE.COM".

Anyone care to comment on what benefit kerberos adds?

Thanks,