Unable to initialize the connection between Oracle and Microsoft LDAP through Pl/Sql

Setups related to Access Control List were taken care by the following scripts in my development environment

BEGIN
    dbms_network_acl_admin.create_acl (
        acl          => 'ldap_access.xml',
        description  => 'Permissions to access LDAP servers.',
        principal    => 'XXXX',
        is_grant     => TRUE,
        privilege    => 'connect'
    );
    COMMIT;
END;

BEGIN
    dbms_network_acl_admin.assign_acl (
        acl        => 'ldap_access.xml',
        host       => 'XXXX.XXX.XXXX.XXXX',
        lower_port => 389,
        upper_port => 389
    );
    COMMIT;
END;

Then I tried to initialize the connection to Microsoft LDAP from Oracle through  the below shown  Pl/Sql code

DECLARE
   ldap_host    VARCHAR2 (512);
   ldap_port    PLS_INTEGER;
   my_session   DBMS_LDAP.SESSION;
BEGIN
   ldap_host := 'XXXX.XXX.XXXX.XXXX';