Joining a NAS to Active Directory

I?ve got a Buffalo Tech tera station II 2.0 TB PRO. The bloody thing refuses to join active directory. I basically get a message from the web interface for the device saying; ?successfully resolved the DNS name but not all services necessary to join the device to the active directory domain were found? when I try joining it to the domain. Anyone know what services need to be running in your domain so this NAS will join it? I already pre added it as a pre-windows 2000 machine but still it won?t join AD. Any thoughts?