Problem with Session ID

I am using the acts_as_authenticated plugin. When a user is
activated, self.current_user = @user, (I hesitate to say "logged_in",
because that is a different action in the account controller), and are
able to click around the site, until they go to one specific
controller, and then the Session ID suddenly changes. They have to
log back in, hitting the "login" action in the account controller.
Once they are logged in this time, everything works perfectly and the
Session ID does not change between the same controllers. I'm not sure
how to track down how or why the Session ID is changing between
controllers, only when the user is on the site after activation.

In my environments.rb file I am using
config.action_controller.session with a :session_key and a :secret.
It seems like the cookie is getting deleted between controllers, or
the session is being reset.

Any ideas where I can look, as I am not very familiar with the session

Thanks in advance!!