Mac 10.8 keeps on asking credentials when accessing a DFS Namespace

When the Mac tries to access the share it keeps on askign it for credentials.

\\domain\Namespace\testdfs\test_dpt\users\username

So the folders have the following permissions

Namespace - Everyone read

Testdfs - User group read

test_dpt- User group read

users - user group read

username - user ID modified.

What can I be missing for the Mac to access this share?

Thanks

Judy