Getting a Fatal Error with Upfront

Hi,, I am getting an error whenever I go to any of the pages on my site...

Fatal error: Class 'WP_Screen' not found in /home/dazhbor/public_html/wp-content/themes/upfront/elements/upfront-this-post/lib/this_post.php on line 515

Can you please help me? the website is http://www.todoparaperros.com.mx

Thanks