As it says in the screenshot: you cannot host the domain name with us because it’s still in use at sitio.com.ar.
Our hosting is running on a platform also used by other hosting providers, so that’s why it’s not possible to host the same domain name with sitio.com.ar and with us.
Do you have an account at sitio.com.ar? If so, please login to your account there and remove your domain name from it. Once you’ve done that, the domain name can be used on our hosting instantly.