Today I had the Kerberos client received a KRB_AP_ERR_MODIFIED error from the server issue again with a different computer. Sure enough, I logged onto the DNS server and there were two A records with different computer names but the same IP address. I guess this might be related, given my previous experience listed in the post above, so I deleted the record with the matching IP address. Hopefully that fixes it. I’ll update this post or add a new one if the problem comes back.