How to setup multi site that will use sub domains in the live server/web server like bluehost

[eluser]rei[/eluser]
At first I have a .htaccess file in the sub directory which my sub domain points to. I removed it because it is denying access when I'm on my localhost. After removing it, it worked then I uploaded the site to a web host and created a subdomain. When I'm on the main site it works and if I set the sub domain as the default app in the CI root index.php ( $application_folder = '../app2'; ) it works. But if I set the main site to be the default app, when I access the sub domain it dont work. It always says Directory access is forbidden.