PHP ldap_bind（）：无法绑定到服务器：凭据无效

Question

I'm connecting ldap server in my local system to server. It is successfully connected but the thing is while connecting from other server ex: B server to A server i got error like this invalid credential.

$username='ZZZ.YYY';
$domain='test';
$host='ldap://AAA.test.org';
$password='XXXX';
$port=389;
$ldapconn = ldap_connect($host, $port)
or die("Could not conenct to {$host}");
if ($ldapconn) {

$bind=ldap_bind($ldapconn, $username .'@' .$domain, $password);
if ($bind) {
    echo("Login correct");
} else {
    echo("Login incorrect");
}

}
ldap_close( $ldapconn );

This code working fine for me . But the same code i pasted in another server just changed the host name for that server and domain name. here i got this error .can you please help me?

$username='ZZZ.YYY';
$domain='test1';
$host='ldap://BBB.test1.org';
$password='XXXX';
$port=389;

$ldapconn = ldap_connect($host, $port)
or die("Could not conenct to {$host}");

if ($ldapconn) {

$bind=ldap_bind($ldapconn, $username .'@' .$domain, $password);

if ($bind) {
    echo("Login correct");
} else {
    echo("Login incorrect");
}

}
ldap_close( $ldapconn );