If you got this php error : "Call to a member function Close() on a non-object " on a Postnuke website for no reasons don't try to fix a problem in the Postnuke Code. The problem comes from the incompatibility between Pn and PHP 5.2.

In order to fix it, you have few ways, one is of course to downgrade your PHP installation, an other one I found on Internet was to add the line

register_shutdown_function('session_write_close');

Just before

session_set_save_handler('pnSessionOpen',

in the <YourPostnukeInstallationDirectory>/includes/pnSession.php

I've done that on all my postnuke websites, working just perfectly !