Error 404 Does Not Get Page

I get the following error. All was well before the site was live, I even changed the url from localhost to my domain on the configuration file. I also set the url helper on the autoload file but still get the same error. Help me please I'm stuck

A PHP Error was encountered
Severity: Error
Message: Call to unknown function base_url ()
File name: html / error_404.php
Number of lines: 14