First of all I'm not into PHP that well anymore but I was asked to update a WordPress website. After updating tot PHP 7.4.33 and the latest version of WordPress (6.6) I got some PHP errors which I cannot get rid of: First error which is shown on the website itself: lessphp fatal error: failed to parse passed in variable @bodyBackground: #2e272f Next when I try to login to the backend I get: lessphp fatal error: failed to parse passed in variable @bodyBackground: #2e272f Warning: Cannot modify header information - headers already sent by (output started at /www/doc/www.grikon.nl/www/wordpress/wp-content/themes/CherryFramework/includes/less-compile.php:155) in /www/doc/www.grikon.nl/www/wordpress/wp-includes/pluggable.php on line 1435 Warning: Cannot modify header information - headers already sent by (output started at /www/doc/www.grikon.nl/www/wordpress/wp-content/themes/CherryFramework/includes/less-compile.php:155) in /www/doc/www.grikon.nl/www/wordpress/wp-includes/pluggable.php on line 1438* Line 155 in the less-compile.php is: } catch (Exception $ex) { echo "lessphp fatal error: ".$ex->getMessage(); } Line 1435-38 in pluggable.php is: /** * Filters the X-Redirect-By header. * * Allows applications to identify themselves when they're doing a redirect. * * @since 5.1.0 * * @param string|false $x_redirect_by The application doing the redirect or false to omit the header. * @param int $status Status code to use. * @param string $location The path to redirect to. */ $x_redirect_by = apply_filters( 'x_redirect_by', $x_redirect_by, $status, $location ); if ( is_string( $x_redirect_by ) ) { header( "X-Redirect-By: $x_redirect_by" ); } header( "Location: $location", true, $status ); return true; } endif; I looked if there is a legacy function used but I can't find anything about it. I also read about less cache files that you should delete with these kind of errors but I can't find those cache files, so that does not seems to be the issue. Can someone help me out with this? Thanks in advance!