Tony on "[Plugin: WordPress SEO by Yoast] XML Parsing Error - syntax error"

In file "class-sitemaps.php"

/wp-content/plugins/wordpress-seo/inc/class-sitemaps.php

This code is in the file
header( 'HTTP/1.1 200 OK', true, 200 );

just put it into comment
//header( 'HTTP/1.1 200 OK', true, 200 );