Problem adding a new subdomain

I couldn't resolve my issue with any previous topics.

I have a working domain. I added a new A record (in DNS manager) "s.mydomain.com". I made a virtual host (for my subdomain "s.mydomain.com" in sites-available):

ServerAdmin email@yahoo.com

ServerName s.mydomain.com

DirectoryIndex index.html

DocumentRoot /var/www/mydomain.com/static

I have enabled the subdomain: a2ensite s.mydomain.com and reloaded the apache.

I get this when I try my subdomain:

While trying to retrieve the URL: http://s.mydomain.com/

The following error was encountered:

Unable to determine IP address from host name for s.mydomain.com

The dnsserver returned:

Name Error: The domain name does not exist.

This means that:

The cache was not able to resolve the hostname presented in the URL.

Check if the address is correct.

Thanks,

Symba