I am not able

I am not able to create save anything on the menu, I was able to create the menu but cant add pages, existing menu is there but cant order or edit or save that menu.
There are a lot of such errors in debug.log
[03-Nov-2017 14:10:00 UTC] WordPress database error Duplicate entry '0' for key 'PRIMARY' for query INSERT INTO wp_postmeta (post_id, meta_key, meta_value) VALUES (6720, '_menu_item_menu_item_parent', '0') made by wp_nav_menu_update_menu_items, wp_update_nav_menu_item, update_post_meta, update_metadata, add_metadata