IP Address Conflict

I am running W2k Advanced Server. I am constantly getting Event 4199 which says that i have an Ip address conflict at a certain MAC address.

I have changed the LAA mac address on the NIC multiple times and the problem still re-occurs.

It is alway the same MAC address that causes the IP conflict. I have identified the equipment causing the equipment but it has a differnet MAC address altogether.

Any solutions in mind? It is my DNS server and we are an ISP, it is proving to be very frustrating now.