If you ever need to rename an application you can follow the directions given here: http://fabien.potencier.org/article/22/a-symfony-tip-rename-a-symfony-application. The directions work well for Symfony version 1.2 but if you are running 1.3+ you will also need to follow these extra steps:

Rename Config File:

 app/app_name/config/<old_app_name>Configuration.class.php TO app/app_name/config/<new_app_name>Configuration.class.php

Edit Config File:

// app/app_name/config/<new_app_name>Configuration.class.php
class <new_app_name>Configuration extends sfApplicationConfiguration

Now just clear cache and load your site through the new controller (new_app_name.php) and it should work as expected.