[horde] Horde Vacation error on Plesk 10: Cannot set vacation notice for mail user: There are no auto-replies set up the mail account.

[Fran - HIS]

  I've installed the Horde vacation module on a Centos5.5 KVM VPS, with 
Plesk10.1.1 and Postfix as MTA
They have Horde 3.3.10 installed (psa-horde)
Horde-DOM is:
  * $Horde: framework/DOM/DOM.php,v 1.9.2.6 2009-10-14 16:42:35 jan Exp $

I installed vacation-1.2.7.1-beta1 from sourceforge.

Horde - vacation is H3-3.2.1

The Horde vacation module is configured to use the Plesk driver, and has 
the Plesk admin username password in it.
I get no error at the configuration stage.

But When I login to webmail.xxxx.xxx as a test user and I try to set up 
a vacation message,  get the error:
"Cannot set vacation notice for mail user emailuserx at xxxx.xxx: There are 
no auto-replies set up for the mail account."

There are no error messages in /var/log/messages or
/var/log/psa-horde/psa-horde.log

I tried Googling around for this error message, but found no result.

What am I missing?

Here is the vacation config:

<?php
/* CONFIG START. DO NOT CHANGE ANYTHING IN OR AFTER THIS LINE. */
// $Horde: vacation/config/conf.xml,v 1.15.2.13 2009/08/18 12:54:49 jan 
Exp $
$conf['vacation']['path'] = '/usr/bin/vacation';
$conf['vacation']['default_subject'] = _("On vacation message");
$conf['vacation']['default_message'] = _("I'm on vacation and will not 
be reading my mail for a while.\nYour mail will be dealt with when I 
return.");
$conf['vacation']['subject'] = true;
$conf['vacation']['from'] = true;
$conf['server']['params']['default']['host'] = localhost;
$conf['server']['params']['default']['user'] = 'xxxxxxxx';
$conf['server']['params']['default']['pass'] = 'xxxxxxxx';
$conf['server']['driver'] = 'plesk';
$conf['aliases']['show'] = true;
$conf['aliases']['driver'] = 'none';
$conf['user']['refused'] = array('root', 'bin', 'daemon', 'adm', 'lp', 
'shutdown', 'halt', 'uucp', 'ftp', 'anonymous', 'nobody', 'httpd', 
'operator', 'guest', 'diginext', 'bind', 'cyrus', 'courier', 'games', 
'kmem', 'mailnull', 'man', 'mysql', 'news', 'postfix', 'sshd', 'tty', 
'www');
$conf['menu']['apps'] = array('imp');
/* CONFIG END. DO NOT CHANGE ANYTHING IN OR BEFORE THIS LINE. */

I'd appreciate your help with this.
(I've also posted to the sork list)

Thank you.

Fran