Call to undefined function get_current_screen()

¡Hi all!

I’ve been googling a lot about that and I couldn’t get any solution that worked.

I’ve recently installed the multisite option as the Codex say, I did all the steps and I’m always getting this error when I try to access the network Dashboard:

Fatal error: Call to undefined function get_current_screen() in /something/somethingelse/www/wp-admin/network/settings.php on line 22

Here’s my .htacess code (the same WP gave me when I did the installation):

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

Thanks.

EDIT: By the way, I’ve installed the sub-domains option, and my installation is in the public directory of my host.