Catch-all: "saslauthd internal error" with kerberos5

[Daniel Norton]

I'm pulling my hair out and getting an error message that seems like a
catch-all for saslauthd, “saslauthd internal error”. Searching around, I
see plenty of people getting the same error message, but with slightly
different problems. None of their solutions is working for me.

Briefly, this works fine:
$ kadmin -p username -w password

But this fails:
$ testsaslauthd -u username -p password
0: NO "authentication failed"

saslauthd works fine with "-a sasldb", but the above is with "-a kerberos5"

This is the most detail I seem to be able to get from saslauthd:

saslauthd[6405]: auth_krb5: krb5_get_init_creds_password: -1765328353
saslauthd[6405]: do_auth : auth failure: [user=username] [service=imap]
[realm=] [mech=kerberos5] [reason=saslauthd internal error]

Kerberos seems happy:
krb5kdc[32128](info): AS_REQ (4 etypes {18 17 16 23}) 127.0.0.1: ISSUE:
authtime 1298779891, etypes {rep=18 tkt=18 ses=18}, username at REALM for
krbtgt/DOMAIN at REALM

I’m running Ubuntu 10.04 (lucid) with the latest updates, namely:
Kerberos 5 release 1.8.1
saslauthd 2.1.23

Thanks for any clues.

--
Daniel