auth_zimbra not initialized

[y@w]

I'm working with a box that's not allowing users to authenticate via SMTP reporting zimbra_auth not initialized in /var/log/zimbra.log whenever I try to authenticate. It turns out that they had installed a new certificate and it didn't get applied to all services - only to the web client. It was just a self-signed certificate so I just regenerated it, but I'm still getting the error. I found this forum thread which lead me to this wiki page, but everything seems to check out..

The certificate is now valid and I checked the config from the wiki page:
$ zmprov gs zimbra.domain.com | grep Auth
zimbraMtaAuthEnabled: TRUE
zimbraMtaAuthHost: zimbra.domain.com
zimbraMtaAuthTarget: TRUE
zimbraMtaAuthURL: https://zimbra.domain.com/service/soap/
zimbraMtaTlsAuthOnly: TRUE

$ zmprov getServer zimbra.domain.com | grep Mode
zimbraMailMode: https

Server is Ubuntu 6.06 running 5.0.2 NE. Anything else I can check?