Subpages not found in Atahualpa theme

I use the Atahualpa theme on my website http://blog.fokkio.nl. I have made two subpages that appear in de navigation bar.
But when I go to the subpage I don’t see the content but only:
“Not Found
Sorry, but you are looking for something that isn’t here.”
It’s very easy to make subpages in Atahualpa, but I can’t get it right
It’s about these two subpages:
http://blog.fokkio.nl/wandelingen/eernewoude
http://blog.fokkio.nl/wandelingen/billie-turf-tocht
I hope someone can help me with this. Thanks so much in advance.