"Fatal error"

Hi, I’m incredibly new to everything, and have recently taken over care of a website run on wordpress. Everything was running fine, until this morning when I tried to install the buddypress plugin and another buddypress plugin for a password protected members only section. As soon as I activated the plugins this message appeared. “Fatal error: Call to undefined function wp_style_add_data() in /home/soicsadmin/soics/wp-content/plugins/buddypress/bp-core/bp-core-cssjs.php on line 99”

I’ve only been given access to edit the site by an online login, which now also won’t work. The site is gone, and I can’t access the dashboard or anything.

Any help at all would be very very very much appreciated!