Errors “rss-feed-post-generator-echo.php on line 5436”

Hi, I'm getting this error when trying to open the plugin. Looks like it's not compatible with DaReactions plugin. Error message: <b>Warning</b>: preg_replace(): Unknown modifier 'k' in <b>/home/customer/www/hotqua.net/public_html/wp-content/plugins/rss-feed-post-generator-echo/rss-feed-post-generator-echo.php</b> on line <b>5436</b> <b>Warning</b>: Cannot modify header information - headers already sent by (output started at /home/customer/www/hotqua.net/public_html/wp-content/plugins/rss-feed-post-generator-echo/rss-feed-post-generator-echo.php:5436) in <b>/home/customer/www/hotqua.net/public_html/wp-content/plugins/da-reactions/classes/DaReactions/User.php</b> on line <b>58</b>   I was hoping to have some help. Thanks!