Fatal error: Uncaught TypeError: call_user_func(): Argument #1 ($callback) must be a valid callback, non-static method GoogleSitemapGeneratorLoader::Enable() cannot be called statically in /homepages/18/d591518518/htdocs/wp-includes/class-wp-hook.php:301 Stack trace: #0 /homepages/18/d591518518/htdocs/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters(NULL, Array) #1 /homepages/18/d591518518/htdocs/wp-includes/plugin.php(470): WP_Hook->do_action(Array) #2 /homepages/18/d591518518/htdocs/wp-settings.php(578): do_action('init') #3 /homepages/18/d591518518/htdocs/wp-config.php(90): require_once('/homepages/18/d...') #4 /homepages/18/d591518518/htdocs/wp-load.php(50): require_once('/homepages/18/d...') #5 /homepages/18/d591518518/htdocs/wp-blog-header.php(13): require_once('/homepages/18/d...') #6 /homepages/18/d591518518/htdocs/index.php(17): require('/homepages/18/d...') #7 {main} thrown in /homepages/18/d591518518/htdocs/wp-includes/class-wp-hook.php on line 301