Domain name is unavailable to access

I'm getting the "Domain Name is Unavailable to Access" error.

I'm trying to use a domain name I bought months ago. I set DNS back then so it's not a propagation issue. I tried with another domain name and gets the same message.

My server is a VPS with a dedicated IP.

On the domain mapping network settings I see this message:

If you are having problems with domain mapping you should try removing the following lines from your wp-config.php file:.

define( 'DOMAIN_CURRENT_SITE', '' );
define( 'PATH_CURRENT_SITE', '/' );
define( 'SITE_ID_CURRENT_SITE', 1 );
define( 'BLOG_ID_CURRENT_SITE', 1 );
Note: If your domain mapping plugin is WORKING correctly, then please LEAVE these lines in place.

I removed these lines as @Ashok said here to see what happens but I get the same error message ("Domain Name is Unavailable to Access").

The sunrise.php file is in the correct folder (/wp-content/). I deleted it in the plugin folder.

Any idea? Thanks!