I'm having a problem with my cart that goes away when I disable the simple SEO url stuff.

I have three top categories on my site. The middle category has several subcategories and the products are in one of those. When I click on that middle category from the main page, I go to a blank page. Not totally blank, but just the body tag is empty. Instead of displaying the category info, it's just empty with a message that there are no products to display in that category.

I also have picture links to the three categories on the main page, and when you click on the middle category there, it works fine.

The other two categories work fine either way.

The problem seems to be intermittent -- I have a hard time replicating it. Might it have something to do with the session / zenid? Seems like it usually works on a return visit and works fine after that.

Can anybody point me in the right direction on this?