Unable to log in RHEL 6.10 host with AD user- Error: pam_ldap: ldap_simple_bind Can't contact LDAP server

Issue

1. While trying to access the server rhel-server which was integrated with AD using nslcd , getting below given error:

Apr 26 16:27:59 rhel-server sshd[22773]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=remote-client  user=aduser
Apr 26 16:27:59 rhel-server sshd[22773]: pam_ldap: ldap_simple_bind Can't contact LDAP server
Apr 26 16:27:59 rhel-server sshd[22773]: pam_ldap: reconnecting to LDAP server...
Apr 26 16:27:59 rhel-server sshd[22773]: pam_ldap: ldap_simple_bind Can't contact LDAP server
Apr 26 16:28:01 rhel-server sshd[22773]: Failed password for aduser from 10.51.0.95 port 26379 ssh2

2. This is /etc/pam.d/password-auth:

auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        sufficient    pam_ldap.so use_first_pass
auth        required      pam_deny.so

account     required      pam_unix.so broken_shadow
account     sufficient    pam_localuser.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     [default=bad success=ok user_unknown=ignore] pam_ldap.so
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3 type=
password    sufficient    pam_unix.so sha512 shadow nullok try_first_pass use_authtok
password    sufficient    pam_ldap.so use_authtok
password    required      pam_deny.so


session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
session     optional      pam_ldap.so

3. This is /etc/openldap/ldap.conf:

URI ldap://adserver.example.com/
BASE o=example

# This is included for pam_ldap.conf
binddn cn=pamproxyuser,ou=admin,o=example
bindpw password
scope sub

ldap_version   3
timelimit      120
bind_timelimit 120
idle_timelimit 3600
bind_policy    soft
deref          never


# DNs in groups
nss_map_attribute uniqueMember member
nss_map_attribute uid shortName
nss_map_attribute userPassword authPassword

nss_initgroups_ignoreusers root daemon bin sys sync games man lp mail news uucp proxy www-data backup list irc gnats nobody libuuid statd sshd puppet


pam_login_attribute              shortName
pam_member_attribute             uniqueMember
pam_password                     nds
pam_password_prohibit_message        Please change your password from your local workstation or the portal.

#ssl start_tls
#ssl on
#TLS_CACERTFILE /etc/ssl/certs/ldap.pem
ssl no