RevSlider Fatal Error Message

It looks like this is a known problem, I just purchased this theme from ThemeForest as my client as a very old version. The RevSlider version that came with the theme is 5.1.6. I am getting the following message when I try to activate the RevSlider plugin:

Fatal error: Uncaught Error: [] operator not supported for strings in /var/www/wp-content/plugins/revslider/includes/framework/base-admin.class.php:71 Stack trace: #0 /var/www/wp-content/plugins/revslider/admin/revslider-admin.class.php(465): RevSliderBaseAdmin::addMetaBox(‘Revolution Slid…’, ”, Array, NULL) #1 /var/www/wp-content/plugins/revslider/admin/revslider-admin.class.php(72): RevSliderAdmin->addSliderMetaBox() #2 /var/www/wp-content/plugins/revslider/admin/revslider-admin.class.php(44): RevSliderAdmin->init() #3 /var/www/wp-content/plugins/revslider/revslider.php(165): RevSliderAdmin->__construct(‘/var/www/wp-con…’) #4 /var/www/wp-admin/includes/plugin.php(2297): include(‘/var/www/wp-con…’) #5 /var/www/wp-admin/plugins.php(191): plugin_sandbox_scrape(‘revslider/revsl…’) #6 {main} thrown in /var/www/wp-content/plugins/revslider/includes/framework/base-admin.class.php on line 71

On the home page – http://tz0.90e.myftpupload.com/home-2/ – it shows the shortcode but again it won’t let me activate the plugin.