Unable to load the requested class: uri

[eluser]sereyous[/eluser]
I have a site setup at http://subdomain.domain.com with the following configurations setup:

Code:

.htaccess
----------------------------------------------------------------------
RewriteEngine on
RewriteCond $1 !^(index\.php|images|uploads|captcha|css|js|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]

config.php
---------------------------------------------
$config['request_protocol'] = 'REQUEST_URI';
$config['base_url']    = "http://subdomain.domain.com/";
$config['index_page'] = "";

I am able to get to the site at http://subdomain.domain.com but when attempting to access any other page I get the following error:

Code:

An Error Was Encountered
Unable to load the requested class: uri

According to the User Guide, this class is supposed to be loaded automatically by CI. I have tried every request protocol option in config.php and none of them work.

Really scratching my head on this one.