I didn’t understand how multisite is installed. Is it installed as a subdomain platform or is it installed on subdomain?
If it is installed on subdomain then subdomain based multisite will not work (as far I know).
If you want to make automatic subdomains creation you will have to install wordpress into /html_public folder, and you will have to add wildcard domain (http://en.wikipedia.org/wiki/Wildcard_DNS_record).
To add wildcard domain go to your cPanel (or whatever you use), navigate to subdomains and add this character as subdomain: *
So… this should be the record: *.your-domain.com