6/6 update: STORE still does not work/error.html extension

I'm just setting my store up and discovered there's a big problem with links. Right now there are only a few items in there in two categories. If you click on one of the two categories displayed on right, like "collectibles", that works fine---the two books listed in that category appear. But then if you click on "all items" to return to main list, you get a page that says no items are in that category.

Somewhere else here I read Danno's message to that clicking on "home" might return one to full listings, so I try that but get the same results.

I want to keep the plain template I chose but am a little concerned about ironing out this glitch, a fix without which my store will not be useful.

Thanks for any help.

here is the store:

http://www.bibliotypebooks.com