kolab driver for roundcube calendar plugin

Hi,

I'm trying to configure roundcube on my running kolab 2.4-server, but I
can't get it running with the kolab-driver. In the calendar-view there
are not calendars available in the list and if I create a new event that
calendar-selection box has no entries.

I have some plugins enabled in roundcube

// List of active plugins (in plugins/ directory)
$rcmail_config['plugins'] = array(
                #'acl',
                'calendar',
                'kolab_addressbook',
                'kolab_folders',
                'kolab_config',
                #'kolab_auth',
                'managesieve',
                'newmail_notifier',
                'password'
        );

Notice, that kolab_auth is disabled, because it told me that it wasn't
able able to contact my ldap server. I hope it's not necessary...

kolab_folders plugin has configured Folders, which exist as
INBOX/Calendar in IMAP/cyrus, so this it:

// Default Calendar folder
$rcmail_config['kolab_folders_event_default'] = 'Calendar';

In mysql I created the tables itipinvitations and kolab_alarms from the
files that came with the plugin.

What the hell do I miss? Any help is appreciated!

regards,
Henning