While moving Website from older Debian 6 to Debian 7 server with Apache I encountered PHP Fatal error:
PHP Fatal error: Call to undefined function session_register() in /var/www2/site/www/include/modules/core/session.class.php on line 7, referer: http://192.168.1.9/
In PHP newer than PHP 5.3, session_register(): function is obsolete, there is no need anymore to have this function initiated before using SESSION variables.
Comment out in PHP files prompting error in Apache error.log everywhere where matched:
session_register();
session_register('session');
to look like this:
//session_register();
//session_register('session');
In newer PHP versions to initialize sessions:
$_SESSION['session']="session_variable";
Before test it again in browser, restart Browser and Apache server to make sure some caching from Apache or Browser doesn't influence. That's all now site works fine 🙂