[eluser]LuckyFella73[/eluser]
You didn't read the thread Jeroen Schaftenaar posted via link!
Line 5 says remove underscore and you left the cookie_domain empty.
Code:
$config['cookie_domain'] = ($_SERVER['SERVER_NAME'] == 'localhost' ? '' : preg_replace('/^www\./', '', $_SERVER['SERVER_NAME']));
I recommend to set cookie encryption to TRUE - don't forget to set the
encryption key in config.php then.