Harry,
following your instruction I changed line 77 with the line you provided. As a result, the wp-admin collapsed and couldn’t get access to the back-end. Got the following message:
add_action
Warning: Cannot modify header information – headers already sent by (output started at /home2/rebelfl1/public_html/wp-content/plugins/yith-woocommerce-popup/includes/newsletter-integration/Mailchimp.php:1) in /home2/rebelfl1/public_html/wp-includes/pluggable.php on line 1210
Any suggestion?