A fix to the issue in CodeIgniter 3.0.3 when working in localhost and the $config['base_url'] is wrong.
Download the MY_Config.php file and put it into the application/core folder of your CodeIgniter project.
If you've set in your config file application/congif/config.php another value than "MY_" in the $config['subclass_prefix'] option, change the name of MY_Config.php replacing "MY_" with your value.
Example:
$config['subclass_prefix'] = 'CUSTOM_';
MY_Config.php => CUSTOM_Config.php