I have inherited this site so not sure of the history. It has Woocommerce installed and all plugins and WP and theme are up to date. The problem is that on the Appearance>Menus page I cannot select any of the other menus to edit. I choose a menu in the drop-down press'select' and am redirected to a 404 page not found page. Also if I click 'new menu' I also get the 404 error. I have never come across this before. I reinstalled WP 3.9.1 to see if that helped, but it did not.