404 error page and sorting by product categories

Hi,

I run internet gallery built on WPEC. I have a problem with 404 error page.

It appears in following cases:
1) when I’m on products page (http://galerialeonardo.com.pl/en/) and click image thumbnail – it doesn’t go to single product page
2) when I’m on artists page (http://galerialeonardo.com.pl/en/artysci/) and click “shop” link
3) when I go to shop settings page and change something in wpec parameters

In other words it has something to do with sorting by product categories.

Usually it helps to turn off and turn on the plugin but it’s very uncomfortable to do it over and over.

I’d be grateful for some help!

http://wordpress.org/plugins/wp-e-commerce/