Missing products on cart summary

[deivishome]

Hello everyone,
I have a online shop created with joomla 1.5 and virtuemart 2.0.20b and i have a problem when buying products, after adding to cart the desired products, in vm cart module are displayed but when i click show cart to display all products and order the purchase, some of them display the prize but not the name of the product. If you want to see it you can go to lueli.es and try to buy something, i repeat in cart module is displayed but not in cart summary. The same happens in the bill.
I tried to upgrade to the latest version but then in the backend virtuemart component shows a white page and in front end it does not work showing eror 404.
I don't know what to do.

Any help appreciated.

Thanks in advance.