Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, non-static method WP_Category_Archive_Widget::register() cannot be called statically in /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/class-wp-hook.php:324 Stack trace: #0 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array) #1 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #2 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/widgets.php(1858): do_action('widgets_init') #3 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/class-wp-hook.php(324): wp_widgets_init('') #4 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters(NULL, Array) #5 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/plugin.php(517): WP_Hook->do_action(Array) #6 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-settings.php(643): do_action('init') #7 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-config.php(106): require_once('/data/sites/web...') #8 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-load.php(50): require_once('/data/sites/web...') #9 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-blog-header.php(13): require_once('/data/sites/web...') #10 /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/index.php(17): require('/data/sites/web...') #11 {main} thrown in /data/sites/web/bowecobe/subsites/boomkwekerijdeneve.be/wp-includes/class-wp-hook.php on line 324