How to fix empty dashboard issue in WordPress?

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:

How can I fix fatal RevSlider error in dashboard after upgrading to PHP 7?

I can access the public side of the site. But the dashboard comes up blank. The log shows an error pointing to the RevSlider plugin: PHP Fatal error: Uncaught Error: [] operator not supported for strings in /var/www/html/wp-content/plugins/revslider/includes/framework/base-admin.class.php:141 Here’s the full trace: #0 /var/www/html/wp-content/plugins/revslider/admin/revslider-admin.class.php(1143): RevSliderBaseAdmin::addMetaBox('Revolution Slid…', '', Array, NULL) #1 /var/www/html/wp-content/plugins/revslider/admin/revslider-admin.class.php(145): RevSliderAdmin->addSliderMetaBox() #2 /var/www/html/wp-content/plugins/revslider/admin/revslider-admin.class.php(87): RevSliderAdmin->init() … Read more