session error

Warning: Unknown(): Your script possibly relies on a session side-effect which existed until PHP 4.2.3.
Please be advised that the session extension does not consider global variables as a source of data,
unless register_globals is enabled. You can disable this functionality and this warning by setting session.
bug_compat_42 or session.bug_compat_warn to off, respectively. in Unknown on line 0

We would need to see your script to tell you whether or not its using deprecated functions.