Additional directory added to URL causing error 404

Hello all,

I’ve been working on a site that uses a shop theme and have run into a problem.

Everything seemed to be working fine but I now get a Error 404 when I click on the checkout.

The checkout page does exist but for some reason an additional directory is added to the URL when you press the checkout button.

Here is the site:

http://www.mixpiks.com/shopde/products/dinos/

Clicking on ‘add to cart’ takes you to this page:

http://www.mixpiks.com/shopde/shopde/?shopping_cart&simpleshop_redir=true

Whereas it should take you here:

http://www.mixpiks.com/shopde/?shopping_cart&simpleshop_redir=true

The directory /shopde/ seems to be doubling up and causing the problem but I don’t know how to fix it.

So over to you. I really hope someone can help and give my thanks in advance.