Root Pages Showing Error 404

I have MarketPress setup on http://samkinggroupsl.com. When you select the root of a product category you get 404 Error (http://samkinggroupsl.com/estore/products/stationary) however when you select any of the individual products pages (http://samkinggroupsl.com/estore/products/stationary/accessories/cork-boards) it works.

So the problem is this

Products (works)
> Stationary (404)
-----------> Accessories (404)
----------------------> Calculators (works)
---------------------------------> etc (works)

Why is this?