Cant get $_SESSION

[eluser]Unknown[/eluser]
!!!SOLVED!!!!
sorry posted 2 minute too fast
solution for futur reference:
http://codeigniter.com/wiki/Native_session/

I work on a system that has been poorly developped, using two technique.
First: PatTemplate
Second: CodeIgniter

Most of the system is done with the first one, But a couple of page where done using codeigniter.
I was asked to redo some part of it, i choose to work with CI.
I need to access a php session variable set from a pattemplate page.
but simply using $_SESSION['VarName'] does not work.
Any idea why?