Warning: Unknown(): Your script possibly relies on a session side-effect which existed until PHP 4.2.3.
Please be advised that the session extension does not consider global variables as a source of data, unless register_globals is enabled.
You can disable this functionality and this warning by setting session.bug_compat_42 or session.bug_compat_warn to off, respectively. in Unknown on line 0

위와 같은 에러가 날 경우
1. 개인서버의 경우
php.ini 에서
register_globals = on 으로 변경

2. 호스팅 서비스를 받는 경우
_head.php 제일 상단에 아래와 같이 코드 삽입

  $_register_globals = (bool) ini_get('register_globals');
  if (!$_register_globals) {
    if (function_exists('ini_set')) {
      ini_set('session.bug_compat_42', 0);
      ini_set('session.bug_compat_warn', 0);
    }
  }