404 error after deploying an app with passenger


I'm desperatly trying to install an app with phusion passenger. I've
already spent 2 days with no success, can somebody help me, please ?
Here is my problem :
I already installed phusion passenger with no problem. It's running on
apache2 on ubuntu 8.10.
I configured everything as mentioned on passenger's website, but i
only get a 404 error, whatever url i try...