PAM LDAP SSH not authenticating users everytime.

[shriram]

I am trying LDAP authentication for users logged by PAM. Also I have disabled(off) nsslapd-anonymous-access flag to restrict anonymous access by providing the binddn and bindpw.
I have changed binddn and bindpw in /etc/ldap.conf for PAM to bind with LDAP to authenticate user.
ie) When a user is trying to ssh pam will be communicated to bind with LDAP by reading /etc/ldap.conf to bind with LDAP to authenticate the corresponding user.
User authentication is not working every time. ie)some time the user is authenticated and sometimes the user is not authenticated.
i have verified the tools 389 FDS, nscd ,sshd, are properly running.
I have tried by doing ldapsearch for the corresponding user. The result shows the user properly.

Thanks
Shriram.