Pro Sites - pageok issue and after subdomain configuration now receive a forbidden error.

On a new wordpress installation using v3.8 I configured as MultiSite with Sub-Domain. DNS wildcard *.domain.com was setup correctly on Godaddy DNS. Then I install successfully Pro Sites plug-in. I manually add a new site named: http://subdomain.domain.com

After install new subdomain the page is open with just; pageok

Reading online I found several people talking regarding an GoDaddy DNS and subdomain issue and I go and manually add the subdomian at the Hosted Domain area:

All Domains
+domain.com
+pro-sites
+subdomain name

After creating the subdomain directory, now I receive a Forbidden error:

Forbidden
You don't have permission to access / on this server.
Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request. Apache Server at http://subdomain.domain.com Port 80

What can be this issue???

A part of the issue above I have a concern about all this...

Let's suppose it's related to a Godaddy (DNS zone configurations, maybe permissions on directories or even subdomain directories needed), what will be happen when new Sites request are taking place by visitors?
Do I need to manually create before hand an alias/subdomain?
How wordpress.com and edublogs.org handle this? I need to be automatically resolved after sites it's created by the visitor. Not by an admin.
How about the verification process regarding if it's available de subdomain or not?

I'm confuse

Anyone pls help.