A site of my company uses blog on WordPress 3.3.1 with theme based on Twenty Ten. Last week I upgraded Apache and PHP on our production server. Afterwards the dashboard refused to work. When a user logs in, a blank dashboard appears. A menu with links is still present, but none of the links work, so one cannot create new posts etc. In the page source I see the following message:
Fatal error: Access to undeclared static property: WP_Screen::$this in blog/wp-admin/includes/screen.php on line 706
There were no changes to WordPress configuration made and no new plugins installed. How to fix the issue?