Quick google pulled this up: http://www.vbulletin.com/forum/archi.../t-246669.html

I've never used Impex before so I can't really be of much help.

Key things in the above that I did note however:
Config.php.new - should be Config.php (obviously).
Make sure all data in Config.php is proper.

If you can't get it to work, repeat the process.