When PHP uses user method for session saving (in my case sharedance) upgrade procedure fails with:
[10-Mar-2010 10:48:44] PHP Fatal error: session_start() [<a href='function.session-start'>function.session-start</a>]: Failed to initialize storage module: user (path: /tmp) in /var/www/html/openx_new/lib/OX/Admin/UI/SessionStorage.php on line 79
In enviroment using comment ( likes instead of uncommented lines the upgrade procedure works. After upgrade
OpenX will work normally with using session.save_handler = user (and sharedance).
Sharedance is found: http://sharedance.pureftpd.org/project/sharedance