[Samba] Unable to join domain with XP: "The parameter is incorrect"

[E P]

I've had a machine set up for some time now running samba 2.something
(or maybe it was upgraded to 3.0.something?  It was up for a long time) 
that recently had some hard drive problems and I had to reinstall.  So 
I did that, and used samba 3.0.10, with the same configuration that I 
had used before (it worked well).

I can join the domain and log in using Windows 2000 with no problems,
but I'm not able to join the domain in Windows XP: when I try to join, 
after I put in my root password (root was added as a samba account) I 
get the error "The following error occurred attempting to join the 
domain "UNIVERSE":  The parameter is incorrect."

I can mount a shared directory on the winXP machine by running (for
example) "\\zarquon\working" and entering the samba user and password 
that I would use to log in.

I've looked around online and verified the following:

- the samba user account was added using smbpasswd
- the samba root account was added using smbpasswd
- the machine was added with the proper $ at the end
- the basic setup appears to work because the win2k machine has no
    trouble joining or logging in
- the registry entry in winXP (requiresignorseal) that used to be
    required is still there (though I understand it's no longer a
    required change)

Some files:

/etc/samba/smbpasswd:
- root:0:<big hash>:[U          ]:LCT-41D1F740:
- epotter:1000:<big hash>:[U          ]:LCT-414C9C10:
- frankie$:1200:<big hash>:[W          ]:LCT-41C60E4F:
- ford$:1200:<big hash>:[W          ]:LCT-41D1F728:

/etc/samba/smb.conf:
- [global]
-    netbios name = ZARQUON
-    workgroup = UNIVERSE
-    server string = Primary Domain Controller
-    hosts allow = 192.168.10. 192.168.20.
-    log file = /var/log/samba/log.%m
-    max log size = 1024
-    security = user
-    encrypt passwords = yes
-    smb passwd file = /etc/samba/smbpasswd
-    unix password sync = Yes
-    passwd program = /usr/bin/passwd %u
-    passwd chat = *New*UNIX*password* %n\n *ReType*new*UNIX*password*
       %n\n *passwd:*all*authentication*tokens*updated*successfully*
-    include = /etc/samba/smb.conf.%m
-    socket options = TCP_NODELAY SO_RCVBUF=32768 SO_SNDBUF=32768
       SO_KEEPALIVE IPTOS_LOWDELAY
-    interfaces = 192.168.10.0/24 192.168.20.0/24
-    local master = yes
-    domain master = yes
-    preferred master = yes
-    domain logons = yes
-    wins support = yes
-    dns proxy = no
-    preserve case = yes
-    short preserve case = yes
-    default case = lower
- <homes, netlogon, shares, etc. follow>

/etc/samba/smb.conf.ford <these are all the same except for logon path>
-    logon path = \\ZARQUON\profiles\%U\winxp
- 
- [profiles]
-    path = /universe/profiles/%U/winxp
-    browseable = no
-    guest ok = no
-    writeable = yes
-    create mask = 0600
-    directory mask = 0700
-    profile acls = yes
-    force user = %U

output of testparm:
- zarquon:/etc/samba# testparm
- Load smb config files from /etc/samba/smb.conf
- Can't find include file /etc/samba/smb.conf.
- Processing section "[homes]"
- Processing section "[netlogon]"
- Processing section "[storage]"
- Processing section "[music]"
- Processing section "[working]"
- Processing section "[programs]"
- Loaded services file OK.
- Server role: ROLE_DOMAIN_PDC
- Press enter to see a dump of your service definitions
- ^C


Any hints?  This one has me stumped.

Thanks
--
Elliott