Website showing error to the visitors

The website shows an error to the visitor. On my front, there is a message popping up at the bottom of the screen. Below is the message that I see on my website:

Notice: ob_end_flush(): failed to send buffer of zlib output compression (0) in /home/risimati/public_html/wp-includes/functions.php on line 5309

The page I need help with: [log in to see the link]