After Install on Server, 404 Errors?

I’ve got several web apps running on CI. I’m moving a new one from my development environment to the server, and for some reason I’m getting 404 errors.

Here’s my index function from my welcome controller:

function index()
{
 redirect('/auth/login/');
        [.....]

The redirect runs but gives me a 404 error. Here’s my file and folder layout:

public_html
--client_folder/
----application/
------cache/
------config/
------controllers/
------core/
------errors/
------helpers/
------hooks/
------index.html
------language/
------libraries/
------logs/
------models/
------third_party/
------views/
----system/

In index.php, I have the following options:

$system_path = 'system';
$application_folder = 'application';

in routes.php, I have the following options:

$route['default_controller'] = "welcome"

in config.php, I have the following options:

$config['base_url'] = "http://" . $_SERVER['HTTP_HOST'] . "/client_folder/";

How can I correct my options so as to avoid the 404 error?

Thanks very much in advance to all for any info.