PHP script unable to access session data if called using ajax

[YesWeCanSayNoToObama]

If i call a php script using ajax im unable to access session variables set by another php script though both scripts are on the same domain, and i have session_start() in both the scripts.If however the php script is called directly it is able to access session variables.Why does this happen ?. Any way to fix the problem ?Please Help.Thank You.