samba - Dec 2008 - Migration from NT4 to Samba PDC : NT_STATUS_INVALID_NETWORK_RESPONSE

Hello,

I want to migrate from an old NT4 PDC to a Samba version 3.0.26a.

My BDC configuration for migration is
[global]
        workgroup = DOMAIN
        server string = %h server Samba %v
        interfaces = eth0, 192.168.1.0/24, lo
        bind interfaces only = Yes
        security = DOMAIN
        map to guest = Bad User
        passdb backend = tdbsam
        passwd program = /usr/bin/passwd %u
        passwd chat = *Enter\snew\sUNIX\spassword:* %n\n
*Retype\snew\sUNIX\spassword:* %n\n
*passwd:*password\supdated\ssuccessfully* .
        unix password sync = Yes
        log level = 4
        syslog = 0
        log file = /var/log/samba.log
        max log size = 1000
        name resolve order = lmhosts hosts wins bcast
        socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
        add user script = /usr/sbin/useradd -g users -c 'SMB Users
Account' -d /dev/null -s /bin/false '%u'
        delete user script = /usr/sbin/userdel -r '%u'
        add group script = /usr/sbin/groupadd '%g'
        delete group script = /usr/sbin/groupdel '%g'
        add user to group script = /usr/bin/gpasswd -a '%u' '%g'
        delete user from group script = /usr/bin/gpasswd -d '%u'
'%g'
        set primary group script = /usr/sbin/usermod -g '%g'
'%u'
        add machine script = /usr/sbin/useradd -g machines -c 'SMB Machine
Account' -d /dev/null -s /bin/false '%u'
        domain logons = Yes
        os level = 33
        preferred master = No
        local master = No
        domain master = No
        dns proxy = No
        wins server = 192.168.1.204
        panic action = /usr/share/samba/panic-action %d
        admin users = root

I can join the NT4 PDC as BDC
net rpc join BDC -S NTSERVER -w DOMAIN -U admin%pwd
Joined domain DOMAIN.

But when I want to vampire or samdup the NT server, I have the following
message
net rpc samdump -S NTSERVER -w DOMAIN -U admin%pwd
[2008/12/17 19:38:39, 0]
rpc_client/cli_pipe.c:cli_rpc_pipe_open_schannel(2679)
  cli_rpc_pipe_open_schannel: failed to get schannel session key from server
NTSERVER for domain DOMAIN.
[2008/12/17 19:38:39, 0] utils/net_rpc.c:run_rpc_command(151)
  Could not initialise schannel netlogon pipe. Error was
NT_STATUS_INVALID_NETWORK_RESPONSE

I have already read many recommended web tuto about NT4 migration.

Any tip would be welcome
Thanks
G?rard