[horde] on refresh horde logs out

[Poornima Marattil]

hi ppl,
im using Horde 2.2.4  with php-4.3.4 on Red Hat Linux AS2.1.
Whenever i refresh or click on the browser back button i get 
logged out.
I don't understand how the session is getting destoryed.
my horde.php
$conf['debug_level'] = E_ALL;
$conf['max_exec_time'] = 0;
$conf['session_name'] = 'Horde';
$conf['cache_limiter'] = 'nocache';
$conf['session_timeout'] = 0;
$conf['use_ssl'] = 2;
$conf['compress_pages'] = true;
$conf['umask'] = 077;
$conf['tmpdir'] = null;
$conf['auth']['driver'] = '';
$conf['auth']['params'] = array();
$conf['log']['enabled'] = true;
$conf['log']['type'] = 'file';
$conf['log']['name'] = '/tmp/horde.log';
$conf['log']['priority'] = LOG_DEBUG;
$conf['log']['ident'] = 'HORDE';
$conf['log']['params'] = array();
$conf['prefs']['driver'] = 'sql';
$conf['prefs']['params'] = array();
$conf['prefs']['params']['phptype'] = 'mysql';
$conf['prefs']['params']['hostspec'] = 'localhost';
$conf['prefs']['params']['username'] = 'horde';
$conf['prefs']['params']['password'] = '######';
$conf['prefs']['params']['database'] = 'horde';
$conf['prefs']['params']['table'] = 'horde_prefs';
$conf['cache']['driver'] = 'file';
$conf['cache']['params'] = array();
$conf['cache']['params']['dir'] = '/var/cache/horde';
$conf['mailer']['type'] = 'smtp';
$conf['mailer']['params'] = array();
$conf['mailer']['params'] = array('auth' => 'true');
$conf['mailer']['params'] = array('host' => 'localhost');
$conf['mailer']['params'] = array('username' => mail);
$conf['mailer']['params'] = array('password' => '@@@@@@@@');
$conf['vfs']['type'] = 'file';
$conf['vfs']['params']['vfsroot'] = '/tmp';
$conf['sessionhandler']['type'] = 'none';
$conf['problems']['enabled'] = false;
$conf['problems']['email'] = 'mailadmin at xyz.com';
$conf['user']['online_help'] = true;
$conf['css']['cached'] = true;
$conf['menu']['floating_bar'] = false;

my php.ini has defaults
session.save_handler = files
session.save_path = /tmp
session.use_cookies = 1
session.auto_start = 0
session.cookie_lifetime = 0 ( until browser is restarted )

other modules im using r IMP 3.2.2, Kronolith 1.1,Mnemo 1.1.

let me know whether more info is required

regards,
poornima