samba - Sep 2004 - Newbie question - Wrong Way to map a share?

After a recent upgrade (details below) as many as 30 percent of our
returning users are  having trouble mapping SAMBA shares of their home
directories on the "terra" server. Many report that the problem
"just
goes away." I've only been able to pin down a couple of them.

Here's what I see. User tries to map the drive, fails, and get a box
with the window:
    Username: terra\Guest
    Password:  ***********

This doesn't work. If I replace terra\Guest  with just the unix
username, it works fine. Everyone says "but it USED to work the other
way. It SHOULD work the other way"

So: *should* it work the other way? What changed? Can I change it
back?  Or do I just need to re-educate all my users? (and take the hit
for making undocumented changes to a production server....) I don't
want to make any changes that would  creating an additional account
for every user or every machine.

I did start with a fresh config file with this installation. 


System is authenticating via NFS and unix passwords, NOT using Active
Directory.
Thanks for a clue bonk,
Betsy. 

PS on the server I see check_ntlm_password:  Authentication for user
[Guest] -> [Guest] FAILED with error NT_STATUS_NO_SUCH_USER

Old box:  Sun 220R  running Solaris 7, samba 2.2.2 and Veritas VM/FS 3.4.
New box: Sun 280R running Solaris 9, samba 3.0.2a and Veritas VM/FS 3.5 
(same Clariion LUN, moved to new box, veritas deport/import-ed.)

Config file:
# Global parameters
[global]
        workgroup = DESIGN
        interfaces = eri0 lo0
        bind interfaces only = Yes
        password level = 8
        log level = 2
        syslog = 7
        log file = /var/adm/smblog
        deadtime = 5
        local master = No
        wins server = 128.103.170.97
        hosts allow = 128.103.170. 128.103.171. 128.103.172. 128.103.173. 128.10
3.174. 128.103.175. 128.103.141. 10.1.1. 10.1.67.
        printing = bsd
        print command = echo
        nis homedir = yes
encrypt passwords = no
posix locking = no
max log size =  524288
[test]
        path = /tmp
        browsable = yes
        valid users = @everyone
        guest ok = Yes
[homes]
        browsable = no
        writable = yes
        create mask = 0775
        directory mask = 0775
 oplocks = no