resolving DNS name to DC in the domain being joined.

i have failed to join windows 7 and 2008 member servers to the domian. i receive the following message.
An attempt to resolve the DNS name of the DC in the domain being joined has failed. please verify this client is configured to reach a DNS server that can resolve DNS names in the target domain.
When i ping the DC i get a reply but when i ping the domain, i dont get a reply.


thank you.