It looks like your server isn't saving session variables properly in general.
I created two pages to demonstrate the issue. If you browse the page: set_session.php it sets a test session variable and links to a page in the member directory to retrieve and display the session variable value. You can see it doesn't work. You should be able to show these pages to your hosting provider and have them fix the underlying problem that your sub-directory doesn't share the same session as your site root.