Please read before setting up a subdomain
To create a subdomain, cPanel asks for the name you wish to use. MAKE SURE the subdomain name you give it doesn't already have a folder named the same. If it does, the subdomain, will not work.
Example: You want to create the subdomain test.yourdomain.com. The subdomain name is test. If there is already a folder in your FTP named test; you need to delete it or rename it to something different before you create the subdomain with the name test from cPanel.