First, you should change the configuration of your php.ini file in order to display errors (it avoids the "die ("Error" . " File: " . __FILE__ . " on line: " . __LINE__)"
Second, the error you got is an error created by your modification (so useless for the understanding of the real trouble ;-)
Either you got an error with the modification of your php.ini file, either you have to add die('dummy') command in others files called at the wrong line (for example, here, you have to go to the authenticate function in the UserSession.php file and add the stop command there.