Fatal Error Call to undefined function wp_json_encode()

I recently install Yoast Seo plugin version 3.3.4 in dashboard . After some time when i try to access my site it shows
Fatal error: Call to undefined function wp_json_encode() in /home/content/y/a/k/yaksophp/html/himalayanholidaysnepal/wp-content/plugins/wordpress-seo/frontend/class-json-ld.php on line 113.

I have no access to edit the code and i am not a programmer. How can i fix this issue?? any suggestion would be greatly appreciated

thanks in advance