警告（2）：session_regenerate_id（）：会话对象销毁失败

I have setup user login in cakephp with Auth. In core.php I have set sessions to be handled like below so that on every page load the session is renewed

Configure::write('Session', array(
    'defaults' => 'cake',
    'timeout' => 180,
    'cookieTimeout' => 1440,
    'checkAgent' => false,
    'autoRegenerate' => true,
    'requestCountdown' => 1
));

Still sometimes I get this warning:

Warning (2): session_regenerate_id(): Session object destruction failed

And after the next click the user is logged out. Any ideas as to why?