Why does my wordpress structure keep failing?

Hi, I’ve been developing a wp site, the only plugins I use are custom post types and post type converter, and the theme is built from scratch, based on a simple theme I used before, with no problems. Everything but the post types creation are coded. Works great.
I built the structure as this: a “published works” post type, with a main category “published works” and 3 child categories: “books”, “magazines” and “bulletins”. Then, I created pages with the same structure, and coded the theme so it shows the lists of all the items in that category and then a single page that shows the selected item in detail.
So, when I go to the “published works” parent page, It shows 6 items of each category, and clicking on one of them takes you to that item in detail. All with thumbnails, etc, very cool. I also included a child pages list on a corner, so you can go directly to the child pages from there, but clicking on “books” there, it gives me a 404 error. I checked the debugging, it said I should include a sidebar page. I included it, but it still 404’s me. Maybe changing the category_names will do, it may be conflicting with the names of the pages,... but nothing. Is there a rule about post types and categories I’m overlooking? (“you shouldn’t do this or this, try this because it conflicts with…” etc?)