What would cause WordPress admin screen to be blank, except for nav bar?

This was the offending code, and it was in wp-admin\includes\screen.php on line 706:

<?php echo self::$this->_help_sidebar; ?>

It should be:

<?php echo $this->_help_sidebar; ?>

http://stackoverflow.com/questions/21614237/what-would-cause-wordpress-admin-screen-to-be-blank-except-for-nav-bar