Hi!
The #1 I already solved the problem! Some php files had blank spaces at end of the file, and I've changed the session... it was 'db' and i changed to ''. Now, this "store" is ok.
some files:
(I've deleted the last blank lines)
Session problem:
PHP Code:
define('STORE_SESSIONS', '');
#2 Sometimes the page seems to be unavaliable (other store)... I don't know if the session expires and causes some error.... sometimes... or it's a server problem... if you want see (its a *** shop): www.freecentersexshop.com.br/loja 
Thank you very much!