samba - Apr 2009 - Unable To Access Samba Share From Linux But Can From Windows

I have successfully installed Samba on several CentOS machines but I am 
having problems attaining complete success on a Ubuntu 8.04 machine.  
The Ubuntu machine's configuration file is very simple and looks like this:

[global]
        server string = Samba Server
        security = USER
        workgroup = workgroup
        log file = /var/log/samba/%m.log
        max log size = 50
        dns proxy = No

[pamuser]
        comment = Secure User's Home Directory
        path = /home/secureuser
        valid users = secureuser
        read only = No

[public]
        comment = Public file sharing space
        path = /home/public
        read only = No
        guest ok = Yes

This machine's name is ubuntu and it is within a network with several 
other Windows machines and one CentOS machine.  The pamuser is a 
passworded pam user. Samba runs successfully in this config except that 
I am unable to access the pamuser's share from the very same ubuntu 
machine using smbclient \\\\ubuntu\\pamuser.  Instead, the following 
error message appears (after password dialog) :

session setup failed: NT_STATUS_LOGON_FAILURE

Otherwise, the above config works fine in that I can access the ubuntu 
pamuser share from the other Windows and CentOS machines and I can also 
access shares on these other machines from the ubuntu machine.

Now, when I then change the security setting to security = SHARE then I 
am again able to access the pamuser ubuntu machine from all other 
Windows machines, however, I cannot access the pamuser share from the 
very same ubuntu machine or the CentOS machine.  With security = SHARE I 
get a different error message as follows:

tree connect failed: NT_STATUS_WRONG_PASSWORD

So, in summary, with security = USER, I can access the pamuser share 
from everywhere (Windows and CentOS) except from the very ubuntu machine 
where the pamuser resides.  Whereas, with security = SHARE, I can access 
the pamuser share from all Windows machines but not from the CentOS 
machine or the ubuntu machine where the pamuser resides.

I have already spent the better part of two days trying to figure this 
out and I have googled it to death.  I hope that a samba expert on this 
list can offer a solution.

Many Thanks,

Gordon Dickens