if I add item to cart, and goto cart first p empty

Actually I think I need just an idea

Infos:
(The category tree, and the add to cart function is working by ajax.)
Everything what I do except I add item to cart everything working fine.
If I add item, and go to cart I get a blank page with a "next" button.
If I click there, or refresh the page everything OK.

So the blank page comes immediately after when I add a product to the cart. I looking for the error for 1 day, but dont found. Any idea?? Or need more description?

Thanks a lot

Ahh not solved. (I removed the last message because that was incorrect)

1. http://powersearchireland.com/shop/
2. login with this: name=teszt, pwd=teszt
3. go to shop, add the first item to cart and go to cart. Its working
4. click to one category on the left, and add a product again, and go to cart again. Its will not working.

Thanks a lot!

The problem was what I recently thought but I searched the problem on wrong place.

Anyway, I get the blank screen because first step is the login but I'm already logged in. The program go to the first step, but It's empty.
So I checked whether or not the user is logged in, and If its true I go to the next step.