Theme menu on live-website

Hi Anders,

Recent you helped me out with a couple of questions regarding a new website. The site was complete and I exported it to a live website, but now there’s something that doesn’t work on the theme anymore.

There are a few menu-items that doesn’t work somehow. It is just a plain page with content, but when you go to them there’s an 404 error page.
You can find the site on https://www.bvheeze.nl. I get this error on the pages ‘de vereniging’, ‘lid worden’ and ‘ contact’.

Hope you can help me out, since the site is already live now ??

Kinds regards,
Angela