warning message when I try to update post or page

I was using plug-in Better WP security. I deatctivated it then uninstalled it and now I get this warning when I try to update a post or page. Warning: Cannot modify header information – headers already sent by (output started at /home/content/b/i/g/bigbuckdoby/html/wp-config.php:29) in /home/content/b/i/g/bigbuckdoby/html/wp-includes/pluggable.php on line 876. Any help would be appreciated. I reinstalled the Better WP security plugin but haven’t activated it.