Next button

Hello, the plugin works great, but I can’t seem to get the next button to load more posts instead it goes to a 404? I’m not quite sure what I’m doing wrong. I have turned on paginate, and have also tried to use WP-PageNavi or Endless scroll, but nothing seems to be able to pull more posts from that category. Thank you.

http://game-jumpers.com/?page_id=67

http://wordpress.org/extend/plugins/posts-in-page/