sessions and subdomains

[eluser]CroNiX[/eluser]

Is the cookie that is created by the session class use URL data to validate it self

Not that I know of. I would guess it has to do with the $config['cookie_domain'] setting, although I haven't checked to see if the session cookies use these values (I assume they would). To use domain-wide, you'd need to make the cookie domain like ".yoursite.com" with a . in front. Then it should work on yoursite.com, www.yoursite.com, es.yoursite.com or whatever.

You can use firebug/firecookie or webkits debugger to see the names, values, domain, expiration, etc, of the cookies to see if they are being set correctly.