Ubuntu has a several kerberos zones preconfigured for MIT and Stanford. I commented them out, even though no instructions ever mention this.
Ubuntu Server 10.04 wasn’t running software to synchronize the time, which had drifted nearly 58 seconds, so I set that up. I hadn’t gotten an error related to this, which I’ve seen other posts mention, but it would eventually be a problem.
I neglected to configure reverse DNS in zeroshell, so I set that up for no real reason other than professionalism. Now it works. I’m guessing it was the DNS, but after all the fruitless labor, I don’t really care.