• Mac OS X Kerberos Extras - MIT Kerberos
• OpenAFS for Mac download - OpenAFS.org
• Utilities (login hooks and the afslocker script)

Also check your /Library/Preferences/edu.mit.Kerberos file, and synchronize your clock with the Kerberos timeserver, time.mit.edu.

If you want to allow Athena users to log in, edit /etc/authorization (under system.login.console, replace authinternal with builtin:krb5authnoverify) and configure LDAP in Directory Access.