Fatal error: Call to a member function insert() on a non-object in /opt/lamp...

app/code/core/Mage/Core/Model/Session/Abstract/Varien.php

// session cookie params
$cookieParams = array(
'lifetime' => $cookie->getLifetime(),
'path' => $cookie->getPath(),
'domain' => $cookie->getConfigDomain(),
'secure' => $cookie->isSecure(),
'httponly' => $cookie->getHttponly()
);

->

// session cookie params
$cookieParams = array(
'lifetime' => $cookie->getLifetime(),
'path' => $cookie->getPath(),
//'domain' => $cookie->getConfigDomain(),
//'secure' => $cookie->isSecure(),
//'httponly' => $cookie->getHttponly()
);