[sork] ldap setting in passwd module

[alex]

Hi all:
Every time i chang passwd from passwd module,i got 
"Warning: LDAP: Unable to bind to server: No such object 
in /usr/local/apache/horde/passwd/lib/Driver/ldap.php on line 55
Could not bind to ldap server "
 
I use openldap 1.2.9 (ldap V.2) as authenticate backend in horde.
In passwd module passwd/conf/config.php and think the 'uid' entry is reason 
that occurs that problem.But i don't know what value should i give to 'uid' in 
ldap Version 2.Any suggestion ?

   'host' => 'ldap.example.com',
   'port' => 389,
   'basedn' => 'cn=root,o=example.com',
   'uid' => 'mail',
   'encryption' => 'crypt'
// );
// If we know the user dn that we want to change we can specify it here.
// That way we can skip the anonymous bind -> search -> rebind process.
// $conf['server']['params']['optional'] = array(
//     'userdn' => 'uid=' . Auth::getAUth() . ',o=example.com'
// );