First make sure you are entering the correct DNS servers for your domain. You can find your hosting account's name servers in your Client Area -> Services -> Product/Service, under the hosting information you will be pointing the domain to.
Some local registrars (.ca for example) have specific requirements for the DNS servers. Sometimes our server's default DNSs are rejected because a requirement is not met.
If this is the case please post a ticket from your here in most cases we will be able to help you.
