Website down

Hello, I’m using Sliding Door and after an update my webpage no longer works:

http://sanjafranic.com

(Fatal error: Cannot redeclare get_the_post_thumbnail_url() (previously declared in /home/vhosting/c/vhost0054985/domains/sanjafranic.com/htdocs/www/wp-includes/post-thumbnail-template.php:190) in /home/vhosting/c/vhost0054985/domains/sanjafranic.com/htdocs/www/wp-content/themes/sliding-door/functions.php on line 217)

The company that hosts the webpage says I should contact you. Thanks so much,

Sanja