[Samba] Win XPPro not connecting to samba domain

[Off_Kilter]

Steps to replicate:

1. Select 'To rename this computer or join a domain, click Change'
2. Select 'Domain' and enter the domain name. Click OK
3. When asked to enter credentials, enter admin user and password. Click OK

This error comes up:

The following error occurred attempting to join the domain "foobar":
The specified domain either does not exist or could not be contacted.

NOTES:
a. If I enter a fake domain in #2 above, it is a different error, it only
asks for user/pass when the correct domain is supplied.
b. Nothing is showing up in the /var/log/samba/log.smbd file when this
happens.