[horde] LDAP Problem!

[Anthony]

Dear All,

I installed a Qmail+Ldap+Courier Server and want to use Horde+IMP ( Horde
2.1 + IMP 3.1 ) for my Web Mail server.

I found that if I don't enable LDAP in Horde+IMP, it worked properly.
However if I configure the Horde+IMP to use LDAP for its backend. The
following errors will shows,

----------------------------------------------------------------------------
--------------
Warning: Undefined offset: 0 in /var/www/html/horde/lib/Prefs/ldap.php on
line 323

Warning: Invalid argument supplied for foreach() in
/var/www/html/horde/lib/Prefs/ldap.php on line 329

Warning: LDAP: modify operation could not be completed. in
/var/www/html/horde/lib/Prefs/ldap.php on line 415

Warning: Cannot add header information - headers already sent by (output
started at /var/www/html/horde/lib/Prefs/ldap.php:323) in
/var/www/html/horde/imp/redirect.php on line 84
----------------------------------------------------------------------------
----------------

The following are my configuration files.

Horde.php
------------------------------------------------------------------
$conf['prefs']['driver'] = 'ldap';
$conf['prefs']['params']['hostspec'] = '172.25.200.12';
$conf['prefs']['params']['port'] = '389';
$conf['prefs']['params']['basedn'] = 'o=abc';
$conf['prefs']['params']['uid'] = 'uid';

$conf['prefs']['params']['rootdn'] = 'cn=admin, o=abc';
$conf['prefs']['params']['username'] = 'admin';
$conf['prefs']['params']['password'] = 'admin';
-------------------------------------------------------------------

slapd.conf
-------------------------------------------------------------------
access to *
                by self write
                by * read
--------------------------------------------------------------------

Pls help!

Thanks!