sessions with IE browser

[sri chitra]

I am trying to set some values in the session
using session.putValue("userId",userId)
and get the values from session using
session.getValue("userId")
It works fine with Netscape browser ver 4.76
but not with IE 5. Sometime it works and sometime it does not work.
I am using IPlanet 4.0 web server.
Do I have to set something in the browser to make it session enabled?
Thanks,
chitra