[horde] Password module with AD.

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Hello list,
I'm getting this error with the password module when I try change the AD password:
2015-10-22T13:35:18+00:00 ERR: HORDE [passwd] Unable to start TLS and unable to fetch rootDSE entry to see if TLS is supported: Can't contact LDAP server
Parameters:
Base: 
Filter: (objectClass=*)
Scope: base [pid 20054 on line 107 of "/usr/share/horde/passwd/lib/Factory/Driver.php"]

 Any idea of where the problem could be? 
is AD a supported directory for the password module?

my .local.php file:
<?php

$backends['ldap'] = array(
    'disabled' => false,
    'name' => 'LDAP Server',
    'driver' => 'Ldap',
    'policy' => array(
        'minLength' => 6,
        'minNumeric' => 1,
    ),
    'params' => array(
        'host' => 'ad.example.local',
        'port' => 636,
        'basedn' => 'OU=Temp,DC=example,DC=local',
        'uid' => 'samaccountname',
        'attribute' => 'unicodePwd',
        'shadowlastchange' => '',
        'shadowmin' => '',
        'realm' => '',
        'filter' => '(objectclass=user)',
        'encryption' => 'plain',
    'referrals' => 0,
        'tls' => true,
    ),
);