The errors indicate that the ordering is fine. This problem should be resolved once the permission issues are fixed; everything indicates that the error output is caused on line 0, which was caused by attempting to open the file and discovering there is no permissions, and then flushing the headers to display the error.
You can also change the location of your session files too by using the
ini_set('session.save_path', '/path/to/your/sessions'); or by modifying a local htaccess / php.ini script. You shouldn't have to do this of course; your host has biffed the permissions on the /tmp directory.
header('HTTP/1.1 420 Enhance Your Calm');