I got this error when second time login to the admin panel of magento ,
frontend works with no issue ,
Any help is appreciated , i disabled cookie in varien.php too like as follows
$cookieParams = array(
'lifetime' => $cookie->getLifetime(),
'path' => $cookie->getPath(),
// 'domain' => $cookie->getConfigDomain(),
// 'secure' => $cookie->isSecure(),
// 'httponly' => $cookie->getHttponly()
);
//
// if (!$cookieParams['httponly']) {
// unset($cookieParams['httponly']);
// if (!$cookieParams['secure']) {
// unset($cookieParams['secure']);
// if (!$cookieParams['domain']) {
// unset($cookieParams['domain']);
// }
// }
// }
and i deleted domain cookies from firebug too .