Some local registrars (.de 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 Customer's area in the corresponding DNS category and explain in details which requirement is not met. In most cases we will be able to help you.
If you are not yet a customer, check out what our domain services include and how we can make your life easier. Managing your own domain is easy when you have the right host by your side.