Error when click quote's edit button

Warning: Cannot modify header information – headers already sent by (output started at /home/website/public_html/wp-content/plugins/flexi-quote-rotator/classes/quote-rotator.class.php:399) in /home/website/public_html/wp-includes/pluggable.php on line 875

http://wordpress.org/plugins/flexi-quote-rotator/