wp-admin.php requires non-existent file?

I fixed the issue by copying the content on admin.php from an earlier version of wordpress, and pasting it onto the admin.php page of the current version.

for reference that code is:
##############################
<?php
/**
* WordPress Administration Bootstrap
*
* @package WordPress
* @subpackage Administration
*/

/**
* In WordPress Administration Panels
*
* @since 2.3.2
*/
if ( ! defined(‘WP_ADMIN’) )
define(‘WP_ADMIN’, TRUE);

if ( ! defined(‘WP_NETWORK_ADMIN’) )
define(‘WP_NETWORK_ADMIN’, FALSE);

if ( ! defined(‘WP_USER_ADMIN’) )
define(‘WP_USER_ADMIN’, FALSE);

if ( ! WP_NETWORK_ADMIN && ! WP_USER_ADMIN ) {
define(‘WP_BLOG_ADMIN’, TRUE);
}

if ( isset($_GET[‘import’]) && !defined(‘WP_LOAD_IMPORTERS’) )
define(‘WP_LOAD_IMPORTERS’, true);

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

if ( get_option(‘db_upgraded’) ) {
$wp_rewrite->flush_rules();
update_option( ‘db_upgraded’, false );

/**
* Runs on the next page load after successful upgrade
*
* @since 2.8
*/
do_action(‘after_db_upgrade’);
} elseif ( get_option(‘db_version’) != $wp_db_version ) {
if ( !is_multisite() ) {
wp_redirect(admin_url(‘upgrade.php?_wp_http_referer=’ . urlencode(stripslashes($_SERVER[‘REQUEST_URI’]))));
exit;
} elseif ( apply_filters( ‘do_mu_upgrade’, true ) ) {
/**
* On really small MU installs run the upgrader every time,
* else run it less often to reduce load.
*
* @since 2.8.4b
*/
$c = get_blog_count();
if ( $c <= 50 || ( $c > 50 && mt_rand( 0, (int)( $c / 50 ) ) == 1 ) ) {
require_once( ABSPATH . WPINC . ‘/http.php’ );
$response = wp_remote_get( admin_url( ‘upgrade.php?step=1’ ), array( ‘timeout’ => 120, ‘httpversion’ => ‘1.1’ ) );
do_action( ‘after_mu_upgrade’, $response );
unset($response);
}
unset($c);
}
}

require_once(ABSPATH . ‘wp-admin/includes/admin.php’);

auth_redirect();

nocache_headers();

// Schedule trash collection
if ( !wp_next_scheduled(‘wp_scheduled_delete’) && !defined(‘WP_INSTALLING’) )
wp_schedule_event(time(), ‘daily’, ‘wp_scheduled_delete’);

set_screen_options();

$date_format = get_option(‘date_format’);
$time_format = get_option(‘time_format’);

wp_reset_vars(array(‘profile’, ‘redirect’, ‘redirect_url’, ‘a’, ‘text’, ‘trackback’, ‘pingback’));

wp_enqueue_script( ‘common’ );
wp_enqueue_script( ‘jquery-color’ );

$editing = false;

if ( isset($_GET[‘page’]) ) {
$plugin_page = stripslashes($_GET[‘page’]);
$plugin_page = plugin_basename($plugin_page);
}

if ( isset($_GET[‘post_type’]) )
$typenow = sanitize_key($_GET[‘post_type’]);
else
$typenow = ”;

if ( isset($_GET[‘taxonomy’]) )
$taxnow = sanitize_key($_GET[‘taxonomy’]);
else
$taxnow = ”;

if ( WP_NETWORK_ADMIN )
require(ABSPATH . ‘wp-admin/network/menu.php’);
elseif ( WP_USER_ADMIN )
require(ABSPATH . ‘wp-admin/user/menu.php’);
else
require(ABSPATH . ‘wp-admin/menu.php’);

if ( current_user_can( ‘manage_options’ ) )
@ini_set( ‘memory_limit’, apply_filters( ‘admin_memory_limit’, ‘256M’ ) );

do_action(‘admin_init’);

if ( isset($plugin_page) ) {
if ( !empty($typenow) )
$the_parent = $pagenow . ‘?post_type=’ . $typenow;
else
$the_parent = $pagenow;
if ( ! $page_hook = get_plugin_page_hook($plugin_page, $the_parent) ) {
$page_hook = get_plugin_page_hook($plugin_page, $plugin_page);
// backwards compatibility for plugins using add_management_page
if ( empty( $page_hook ) && ‘edit.php’ == $pagenow && ” != get_plugin_page_hook($plugin_page, ‘tools.php’) ) {
// There could be plugin specific params on the URL, so we need the whole query string
if ( !empty($_SERVER[ ‘QUERY_STRING’ ]) )
$query_string = $_SERVER[ ‘QUERY_STRING’ ];
else
$query_string = ‘page=’ . $plugin_page;
wp_redirect( admin_url(‘tools.php?’ . $query_string) );
exit;
}
}
unset($the_parent);
}

$hook_suffix = ”;
if ( isset($page_hook) )
$hook_suffix = $page_hook;
else if ( isset($plugin_page) )
$hook_suffix = $plugin_page;
else if ( isset($pagenow) )
$hook_suffix = $pagenow;

set_current_screen();

// Handle plugin admin pages.
if ( isset($plugin_page) ) {
if ( $page_hook ) {
do_action(‘load-‘ . $page_hook);
if (! isset($_GET[‘noheader’]))
require_once(ABSPATH . ‘wp-admin/admin-header.php’);

do_action($page_hook);
} else {
if ( validate_file($plugin_page) )
wp_die(__(‘Invalid plugin page’));

if ( !( file_exists(WP_PLUGIN_DIR . “/$plugin_page”) && is_file(WP_PLUGIN_DIR . “/$plugin_page”) ) && !( file_exists(WPMU_PLUGIN_DIR . “/$plugin_page”) && is_file(WPMU_PLUGIN_DIR . “/$plugin_page”) ) )
wp_die(sprintf(__(‘Cannot load %s.’), htmlentities($plugin_page)));

do_action(‘load-‘ . $plugin_page);

if ( !isset($_GET[‘noheader’]))
require_once(ABSPATH . ‘wp-admin/admin-header.php’);

if ( file_exists(WPMU_PLUGIN_DIR . “/$plugin_page”) )
include(WPMU_PLUGIN_DIR . “/$plugin_page”);
else
include(WP_PLUGIN_DIR . “/$plugin_page”);
}

include(ABSPATH . ‘wp-admin/admin-footer.php’);

exit();
} else if (isset($_GET[‘import’])) {

$importer = $_GET[‘import’];

if ( ! current_user_can(‘import’) )
wp_die(__(‘You are not allowed to import.’));

if ( validate_file($importer) ) {
wp_redirect( admin_url( ‘import.php?invalid=’ . $importer ) );
exit;
}

// Allow plugins to define importers as well
if ( !isset($wp_importers) || !isset($wp_importers[$importer]) || ! is_callable($wp_importers[$importer][2])) {
if (! file_exists(ABSPATH . “wp-admin/import/$importer.php”)) {
wp_redirect( admin_url( ‘import.php?invalid=’ . $importer ) );
exit;
}
include(ABSPATH . “wp-admin/import/$importer.php”);
}

$parent_file = ‘tools.php’;
$submenu_file = ‘import.php’;
$title = __(‘Import’);

if (! isset($_GET[‘noheader’]))
require_once(ABSPATH . ‘wp-admin/admin-header.php’);

require_once(ABSPATH . ‘wp-admin/includes/upgrade.php’);

define(‘WP_IMPORTING’, true);

if ( apply_filters( ‘force_filtered_html_on_import’, false ) )
kses_init_filters(); // Always filter imported data with kses on multisite.

call_user_func($wp_importers[$importer][2]);

include(ABSPATH . ‘wp-admin/admin-footer.php’);

// Make sure rules are flushed
global $wp_rewrite;
$wp_rewrite->flush_rules(false);

exit();
} else {
do_action(“load-$pagenow”);
// Backwards compatibility with old load-page-new.php, load-page.php,
// and load-categories.php actions.
if ( $typenow == ‘page’ ) {
if ( $pagenow == ‘post-new.php’ )
do_action( ‘load-page-new.php’ );
elseif ( $pagenow == ‘post.php’ )
do_action( ‘load-page.php’ );
} elseif ( $pagenow == ‘edit-tags.php’ ) {
if ( $taxnow == ‘category’ )
do_action( ‘load-categories.php’ );
elseif ( $taxnow == ‘link_category’ )
do_action( ‘load-edit-link-categories.php’ );
}
}

if ( !empty($_REQUEST[‘action’]) )
do_action(‘admin_action_’ . $_REQUEST[‘action’]);

?>
###########################

Doing so fixes the issue.

I can confirm that the original download which I downloaded twice had that line on line 12.

However when I download today, it does not. Not sure if it is the mirror I downloaded from, or if it is fixed across the board. The admin.php file that I downloaded today however contains code that functions properly.