Just open persistent_login.module file in any of your favorite editor.
then look for persistent_login_menu()

and change that with this:

function persistent_login_menu() {
$items = array();
$items['persistent_login/erase'] = array(
'page callback' => 'persistent_login_erase',
'access callback' => 'user_access',
'access arguments' => array('administer Persistent Login'),
'type' => MENU_CALLBACK);

$items['admin/settings/persistent_login'] = array(
'title' => t('Persistent Login'),
'description' => t('Control Persistent Login session lifetime and restricted pages.'),
'page callback' => 'drupal_get_form',
'page arguments' => array('persistent_login_admin_settings'),
'access callback' => 'user_access',
'access arguments' => array('administer Persistent Login'),
'type' => MENU_NORMAL_ITEM);
return $items;
}
after changing this function
open your settings.php file in sites/default folder
look for this
ini_set('session.cookie_lifetime', 200000);
if value is 0 then let that be like that else change that 200000 to 0.
thereafter you should login as admin and navigate to admin/settings/persistent_login to set your login settings.
Hope this solves your problem.