[imp] mysql session

[Barti]

I have problem with setup mysql session
I changed in horde.php

$conf['sessionhandler']['type'] = 'external';
and

 $conf['sessionhandler']['params'] = array();
 $conf['sessionhandler']['params']['phptype'] = 'mysql';
 $conf['sessionhandler']['params']['hostspec'] = 'localhost';
 $conf['sessionhandler']['params']['username'] = 'horde';
 $conf['sessionhandler']['params']['password'] = '*******';
 $conf['sessionhandler']['params']['database'] = 'horde';
 $conf['sessionhandler']['params']['table'] = 'horde_sessionhandler';

but see blank screen after entering main page
no error
any sugestion?