DHCP error message

I don't know what NT version and service pack you are running but I am assuming you are running NT 4 on your network.
Windows NT 4.0 SP2 DHCP servers issue a DHCPNACK to any DHCPREQUEST that does not appear to be valid for the subnet. This problem occurs when you are using multiple logical IP subnets (multinetting) and two DHCP servers on the same physical network are serving two different logical subnets.
For example, a client broadcasts DHCPREQUEST and receives ACK from server A and NACK from server B. Because there is no communication between server B and server A, server B is not aware of the existence of server A. If it does not send a NACK, then a client who has just moved to this network will never know that its old address is invalid.
To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, please see the following article in the Microsoft Knowledge Base:http://support.microsoft.com/support/kb/articles/Q152/7/34.ASP