Machine:  Dell 2950
Operating system:  Red Hat Enterprise Linux version 5.2, 64-bit

We use Samba to authenticate and authorize users to gain access to our Linux servers.  User account info and credentials reside on Windows Active Directory (LDAP) servers.

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Problem:  Apparently pam_winbind fails to get the credentials for any AD user
          account for any application that requires user authentication and
          authorization hence no AD user can use the system.

Pertinent log messages from /var/log/secure:

--------------------------------------------------------------------------------
Jan 16 12:15:46 democracy sshd[31902]: Invalid user dg7108 from 134.240.18.70
Jan 16 12:15:46 democracy sshd[31903]: input_userauth_request: invalid user dg7108
Jan 16 12:16:00 democracy sshd[31902]: pam_winbind(sshd:auth): getting password (0x00000000)
Jan 16 12:16:00 democracy sshd[31902]: pam_winbind(sshd:auth): pam_winbind_request: write to socket failed!
Jan 16 12:16:00 democracy sshd[31902]: pam_winbind(sshd:auth): internal module error (retval = 3, user = 'dg7108')
Jan 16 12:16:00 democracy sshd[31902]: pam_unix(sshd:auth): check pass; user unknown
Jan 16 12:16:00 democracy sshd[31902]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=usmawkddth17620.eecs.usma.edu 
Jan 16 12:16:00 democracy sshd[31902]: pam_succeed_if(sshd:auth): error retrieving information about user dg7108
Jan 16 12:16:02 democracy sshd[31902]: Failed password for invalid user dg7108 from 134.240.18.70 port 44485 ssh2
Jan 16 12:16:10 democracy sshd[31902]: pam_winbind(sshd:auth): getting password (0x00000000)
Jan 16 12:16:10 democracy sshd[31902]: pam_winbind(sshd:auth): pam_winbind_request: write to socket failed!
Jan 16 12:16:10 democracy sshd[31902]: pam_winbind(sshd:auth): internal module error (retval = 3, user = 'dg7108')
Jan 16 12:16:10 democracy sshd[31902]: pam_unix(sshd:auth): check pass; user unknown
Jan 16 12:16:10 democracy sshd[31902]: pam_succeed_if(sshd:auth): error retrieving information about user dg7108
Jan 16 12:16:13 democracy sshd[31902]: Failed password for invalid user dg7108 from 134.240.18.70 port 44485 ssh2
Jan 16 12:16:15 democracy sshd[31903]: Connection closed by 134.240.18.70
Jan 16 12:16:15 democracy sshd[31902]: PAM 1 more authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=usmawkddth17620.eecs.usma.edu
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No apparent build or installation messages were observed.

All proper configuration was done. 

NOTE:  We have about 20 other Linux servers running a 32-bit version of this
operating system in which Samba has worked very well for 4-5 years.  This is the
only 64-bit Linux server we have which I just stood up.

Except for the authentication piece other parts of Samba do work:

Logged in as local root:

1.  I can get the correct output for:  wbinfo -n <AD_USER>

2.  cd ~<AD_USER>

3.  getent passwd <AD_USER> produces the correct output.

On a AD windows PC or Laptop I can map my Linux account directory to the 
windows machine logical drive.

I have tried different versions:  3.0.28a, 3.0.31, 3.0.33, 3.2.7
All with the same result.