Error when trying to acces my website.

Hi there, folks over at WPMUDEV! When I try to access my website, it gives me the following error: Fatal error: Call to undefined function add_shortcode() in /home/hogiedes/public_html/wp-includes/class-wp-embed.php on line 36

Do you guys have any idea what it could mean, and how to fix it? I can't acces my website anymore at all which is certainly not nice. Please answer, fast!