update message: Fatal error: Call to undefined function wp_get_current_user() in /home/admin/public_

Hi,

When trying to update: http://www.campus-lingua.com/wp-admin/network/update-core.php

I get this message.

Fatal error: Call to undefined function wp_get_current_user() in /home/admin/public_html/wp-includes/capabilities.php on line 1028

I tried deactivating all the plugins but that doesn't seem to help.

Suggestions? I saw somewhere someone suggested a manual update. Is that the solution?