How do I "fix" a wp-blog-header.php error message?

I recently updated a site and received the following error message:

Fatal error: Call to undefined function wp() in /home/atlmp/public_html/wp-blog-header.php on line 14

I checked the file and there doesn’t seem to be any issues, so I can’t figure out what’s wrong?

<?php
/**
 * Loads the WordPress environment and template.
 *
 * @package WordPress
 */

if ( !isset($wp_did_header) ) {

  $wp_did_header = true;

  require_once( dirname(__FILE__) . '/wp-load.php' );

  wp();

  require_once( ABSPATH . WPINC . '/template-loader.php' );

}

?>

Any help would be greatly appreciated.