samba - Aug 2002 - Why can't my backup user log in to the share?

I'm trying to work out why I have the following problem, and I'd really 
appreciate any help you guys can offer:

I have a samba share mapped as drive o: to an NT4 server, which happens to 
be the machine that takes our backups. What I want to do is back up the 
data on the Samba share too. Simple enough, you'd ahve thought, and I can 
back up stuff from a Windows share fine. But, whether or not I have the 
share correctly mapped to and working on the NT4 machine, the backups 
regularly fail with messages like "logon failure" and occasionally 
"unexpected network error". Trying to map a network drive on a Windows
machine using the backup server's username/password gives me 'Incorrect 
password or unknown username'. The UNIX user arcserve does exist, though 
it's 'arcserve' not 'ArcServe' (as it is on Windows).

Running smbclient with the backup user name on the Samba server itself gives:

smbclient \\\\samba\\art -U arcserve
added interface ip=127.0.0.1 bcast=127.255.255.255 nmask=255.0.0.0
added interface ip=172.17.1.3 bcast=172.17.255.255 nmask=255.255.0.0
session request to SAMBA failed (Called name not present)
Password:
session setup failed: NT_STATUS_LOGON_FAILURE

I _thought_ I had authorisation and automatic user creation sorted out in 
my smb.conf and it seems to be working for most other users; despite the 
error message I do seem to be getting a connection to somewhere. What I 
most don't know how to do, though, is go about debugging this - fid out 
where I'm connecting to and so on. My smb.conf is below, can anyone help?

Many thanks,
Vicky Clarke

[global]

;        netbios name = SAMBA
         workgroup = DOMAIN1

# The following is excessively paranoid, but until a solid solution to the 
netwo
rk browsing and reliable
# mapping of network drives issue is arrived at we'll leave it be.

         domain master = no
         local master = no
         preferred master = no

         browseable = yes
         os level = 2
         wins server = 172.17.1.2
         hosts allow = 172.17.1.2 172.17.3. 127.
         interfaces = 172.17.1.3/255.255.0.0
         encrypt passwords = yes
         guest account = Nobody
         map to guest = Bad User
         add user script = /usr/sbin/useradd %u
         delete user script = /usr/sbin/userdel %u
         unix password sync = yes
         passwd program = /usr/bin/passwd %u
         passwd chat = "New password:*" %n\n "Re-enter new
password:*" %n\n
"Pass
word changed*"

# This tells samba to write log files per machine.
         log file = /var/log/samba/%m
# This sets an alternate log level. Default is 2.
         log level = 10

# Uncomment the following, if you want to use an existing NT-Server to
# authenticate users, but don't forget that you also have to create them
# locally!
         security = domain
         password server = 172.17.1.2
         socket options = SO_KEEPALIVE IPTOS_LOWDELAY TCP_NODELAY

         local master = No

         interfaces = lo eth0

         wins support = no
         # 'yes' doesn't work; 'no' does work

         wins server = 172.17.1.2

         character set = ISO8859-15
         client code page = 850

         veto files = /*.eml/*.nws/riched20.dll/*.{*}/
[vicky]
         comment = Linux home directory for Vicky
         browseable = no
         valid users = vclarke root Administrator
         path = /home/vclarke
         read only = no
         create mask = 0600
         directory mask = 0700

[homes]
         comment = User home directory
         path = /share/pchomes/%S
         read only = No
         create mask = 0640
         directory mask = 0750
         browseable = No
         writeable = yes
#       nt acl support = yes


# Create a general-purpose shared directory everyone can use

[art]
         comment = Art directories
         path= /share/art
         writeable = yes
         create mask = 0666
         directory mask = 0775
         nt acl support = yes
         admin users = smbbackup
         mangled names = yes