Using Import Product Function creates havoc

I am trying to mass import products(Sessions) to marketpress. If you visit my site you will notice that there are crazy things happening with Product catagories. For instance this product categories link actually takes you to the first product. http://iblog.dearbornschools.org/pd/sessions/sessions/category/early-am-k-1st-grade/

On this page the First Item shows the product category but none of the others do. http://iblog.dearbornschools.org/pd/sessions/sessions/category/2nd-3rd-grade/

What gives? I cannot make heads or tails of this.