Always remember that the Menus and pages in WordPress are separate entities.
Therefore if you delete a page it may still be in your sites main navigation creating a not found error when someone clicks.
Here is how to remedy that.
- In WordPress admin mouse over “appearance” on the left and select “menus” from the pop-out list.
- On the right-hand side, you will see a list of bars which represent menu items on your main site.
- Find the menu item you want to remove it will be the title of the page.
- Click the small downward pointing arrow at the end of that menu item
- Click The Remove link
- Click “Save Menu” top right of the page.
Now go back to your site and you will see that menu item is no longer there.