Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method category_excluder::register() cannot be called statically in /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/class-wp-hook.php:287
Stack trace:
#0 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#1 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#2 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/widgets.php(1765): do_action('widgets_init')
#3 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/class-wp-hook.php(287): wp_widgets_init('')
#4 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#5 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#6 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-settings.php(540): do_action('init')
#7 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-config.php(96): require_once('/customers/f/3/...')
#8 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-load.php(37): require_once('/customers/f/3/...')
#9 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-blog-header.php(13): require_once('/customers/f/3/...')
#10 /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/index.php(17): require('/customers/f/3/...')
#11 {main}
  thrown in /customers/f/3/6/malen-macht-spass.de/httpd.www/malkurs-acryl/wp-includes/class-wp-hook.php on line 287