Disable Kerberos / Single Sign-on
To disable Kerberos, open Terminal at Mac mini and enter the following command:

sudo sso_util remove -k -a username -p password -r YOUR.KERBEROS.REALM


Replace username, password with the user name and password of the Open Directory administrator (user/password with admin rights on Mac mini). It seems that YOUR.KERBEROS.REALM is "LKDC".

The Open Directory Overview pane of Server Admin (at Mac mini) should show the Kerberos service status as stopped.

Source