I've included "cf.captcha.php" on my "index.php" file and sometimes (not everytime) I get that error when I have to validate the captcha:
[06-Mar-2015 18:39:57 UTC] PHP Warning: Cannot modify header information - headers already sent by (output started at /home/path/to/index.php:17) in /home/path/to/captcha/cf.captcha.php on line 88
What if instead of
setcookie('Captcha', '', time() - 3600, '/',$domain);
if (isset($_COOKIE['Captcha'])) unset($_COOKIE['Captcha']);
Would that work without errors?
I suppose with the code above you're trying to remove the cookie, but I guess unset