Cannot modify header information

Hi,

I am suddenly getting a “Cannot modify header information” error message whenever I try to publish or update a post, even though I have not changed anything on the website other than changing the max_input_vars inside the php.ini.

Of course, I have reversed this change but the “Cannot modify header information” error was not resolved.

The exact error message is as follows:

Warning: Cannot modify header information – headers already sent by (output started at /home/geschic8/public_html/wp-includes/functions.php:1476) in /home/geschic8/public_html/wp-admin/post.php on line 198

Warning: Cannot modify header information – headers already sent by (output started at /home/geschic8/public_html/wp-includes/functions.php:1476) in /home/geschic8/public_html/wp-includes/pluggable.php on line 1216

I have searched everywhere but only found cases where some plugin was directly mentioned inside the error message. In my case, the error message seems to say there is a problem with the /wp-includes/functions.php but I have not made any changes to the core.. I have also deactivated all recently installed or modified plugins.

I have also found cases where it was suggested that this is caused by whitespaces or closing php tags inside the files mentioned in the error message.
I have checked the functions.php, the post.php and the pluggable.php and have found no whitespaces or anything else at the end after the }.

The post.php has the following code on from line 196 to 199:

// Session cookie flag that the post was saved
	if ( isset( $_COOKIE['wp-saving-post'] ) && $_COOKIE['wp-saving-post'] === $post_id . '-check' ) {
		setcookie( 'wp-saving-post', $post_id . '-saved', time() + DAY_IN_SECONDS, ADMIN_COOKIE_PATH, COOKIE_DOMAIN, is_ssl() );
	} 

Line 198 inside post.php is exactly this:
setcookie( 'wp-saving-post', $post_id . '-saved', time() + DAY_IN_SECONDS, ADMIN_COOKIE_PATH, COOKIE_DOMAIN, is_ssl() );

The pluggable.php has the following code on from line 1160 to 1220:

if ( !function_exists('wp_redirect') ) :
/**
 * Redirects to another page.
 *
 * Note: wp_redirect() does not exit automatically, and should almost always be
 * followed by a call to <code>exit;</code>:
 *
 *     wp_redirect( $url );
 *     exit;
 *
 * Exiting can also be selectively manipulated by using wp_redirect() as a conditional
 * in conjunction with the {@see 'wp_redirect'} and {@see 'wp_redirect_location'} hooks:
 *
 *     if ( wp_redirect( $url ) ) {
 *         exit;
 *     }
 *
 * @since 1.5.1
 *
 * @global bool $is_IIS
 *
 * @param string $location The path to redirect to.
 * @param int    $status   Status code to use.
 * @return bool False if $location is not provided, true otherwise.
 */
function wp_redirect($location, $status = 302) {
	global $is_IIS;

	/**
	 * Filters the redirect location.
	 *
	 * @since 2.1.0
	 *
	 * @param string $location The path to redirect to.
	 * @param int    $status   Status code to use.
	 */
	$location = apply_filters( 'wp_redirect', $location, $status );

	/**
	 * Filters the redirect status code.
	 *
	 * @since 2.3.0
	 *
	 * @param int    $status   Status code to use.
	 * @param string $location The path to redirect to.
	 */
	$status = apply_filters( 'wp_redirect_status', $status, $location );

	if ( ! $location )
		return false;

	$location = wp_sanitize_redirect($location);

	if ( !$is_IIS && PHP_SAPI != 'cgi-fcgi' )
		status_header($status); // This causes problems on IIS and some FastCGI setups

	header("Location: $location", true, $status);

	return true;
}
endif;

Line 1216 inside pluggable.php is exactly this:
header("Location: $location", true, $status);

So, does any of this make sense to you?

Thanks in advance and best regards,
Jascha

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