Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method Multilevel_Navigation_Menu_WP::mnmwp_register_menu() cannot be called statically in /customers/d/3/b/ettbrasseri.se/httpd.www/wp-includes/class-wp-hook.php:308
Stack trace:
#0 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters(NULL, Array)
#1 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#2 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-settings.php(617): do_action('init')
#3 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-config.php(118): require_once('/customers/d/3/...')
#4 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-load.php(50): require_once('/customers/d/3/...')
#5 /customers/d/3/b/ettbrasseri.se/httpd.www/wp-blog-header.php(13): require_once('/customers/d/3/...')
#6 /customers/d/3/b/ettbrasseri.se/httpd.www/index.php(17): require('/customers/d/3/...')
#7 {main}
  thrown in /customers/d/3/b/ettbrasseri.se/httpd.www/wp-includes/class-wp-hook.php on line 308