404 Error

I have create a page called 'Search by' which I have added to the parent page of 'People'.

http://www.thrivenetwork.co.uk/people/search-by-2/

For some reason I get a 404 error when I visit the page. If I move the page out from under People it loads properly and also loads properly if I made the "News" page it's parent. What do you think the issue is?