[imp] Fatal error - can not list users

[Robert Carnecky]

I try to list users from my Cyrus IMAP server and I get the error :

Too many login failures
[line 236 of /big/httpd/htdocs/horde/admin/user.php]

and later in the error array I can see

array(6) {
       ["file"]=>
       string(48) "/big/httpd/htdocs/horde/lib/Horde/IMAP/Admin.php"
       ["line"]=>
       int(197)
       ["function"]=>
       string(8) "_connect"
       ["class"]=>
       string(10) "imap_admin"
       ["type"]=>
       string(2) "->"
       ["args"]=>
       array(0) {
       }

seems to be authentication problem. I am using imp to authenticate Horde 
users, Cyrus IMAP server uses LDAP authentication. I can list all user 
mailboxes in the Mail folder and the horde admin user can use cyradm 
utility to modify IMAP server. I am using imp 4.0.3 and horde framework 
4.0.5. Any hints?

Regards
Robert