hi, i can one question.
How to share session state across subdomains for ex: shop.domein.com and domein.com
i check this
as long as the subdomains are on the same server i dont see a problem, i use subdomain and sessions are working perfectly.
Check the Path of the PHPSESSID cookie, the only problem i can think of
Sometime the problem with sessoin and domains comes from your php configuration.
That mays help: http://stackoverflow.com/questions/644920/allow-php-sessions-to-carry-over-to-subdomains