how to config Codeigniter shopping cart to work on subdomains

[eluser]chiste[/eluser]
I'm working on a Multi Site installation of PyroCMS 1.3.2. I have create 3 sites:

The Default site is on my primary domain for the Spanish version, and I have 2 other sites for Italian and English versions of the site on a corresponding subdomain for each one like this:

http://arbioperu.org (spanish)
http://italiano.arbioperu.org
http://english.arbioperu.org

I have create a PyroCMS Module with Codeigniter Shopping Cart Class wich works fine on my primary domain but dosent work on the subdomain sites. nothing is added to the cart.

I think it my be a problem with the coockies setup.

Thanks for your advice