I have enabled mod_rewrite on my server and it successfully rewrites URL's and works nicely, but then it logs the URL to be rewritten as "File does not exist" .... in the error log

My http.conf section

Code:
<VirtualHost *:80>
    ServerName customers.foo.com
    ServerAdmin webmaster@foo.com
    DocumentRoot /var/www/portal
    RewriteEngine On
    RewriteCond %{SERVER_PORT}
...