Membership register page send error

On my site on register page http://***news.net/register-monthly/ I get this error during register:
Cannot modify header information - headers already sent by (output started at /wp-content/plugins/wpmu-dev-seo/includes/tools/onpage.php:74) in /wp-includes/pluggable.php on line 1216

I double check plugin/theme conflict and I found that membership have some issue with Addon Library for Visual Composer