Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method runPHP::DetermineAllEvaldPosts() cannot be called statically in /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/class-wp-hook.php:288 Stack trace: #0 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/class-wp-hook.php(312): WP_Hook->apply_filters(NULL, Array) #1 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/plugin.php(478): WP_Hook->do_action(Array) #2 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/general-template.php(2879): do_action('wp_head') #3 /customers/d/7/1/chirozuun.be/httpd.www/wp-content/themes/zerif-lite/header.php(20): wp_head() #4 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/template.php(722): require_once('/customers/d/7/...') #5 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/template.php(671): load_template('/customers/d/7/...', true) #6 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/general-template.php(41): locate_template(Array, true) #7 /customers/d/7/1/chirozuun.be/httpd.www/wp-content/themes/zerif-lite/404.php(7): get_header() #8 /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/template-loader.php(98): include('/customers/d/7/...') #9 /customers/d/7/1/chirozuun.be/httpd.www/wp-blog-header.php(19): require_once('/customers/d/7/...') #10 /customers/d/7/1/chirozuun.be/httpd.www/index.php(17): require('/customers/d/7/...') #11 {main} thrown in /customers/d/7/1/chirozuun.be/httpd.www/wp-includes/class-wp-hook.php on line 288