On a TCP/IP network, the addresses have to be maintained by the system admins -- that's you. Addresses can be doled out in two ways -- manually or automatically. Manual methods involve assigning an IP address and then keeping track to make sure that you don't assign it twice. The Automatic method most commonly used is DHCP, in which you configure a block of addresses to be assigned to users, and then allow the DHCP service to assign them. A common mistake is in allocating a permanent address manually that exists in the DHCP range.
To resolve:
Get yourself a big sheet of paper, and start visiting each computer. Run IPCONFIG on each one and look for sections like this:
Ethernet adapter Local Area Connection:
DHCP Enabled. . . . . . . . . . . : Yes
IPv4 Address. . . . . . . . . . . : 192.168.1.27(Preferred)
Subnet Mask . . . . . . . . . . . : 255.255.255.0
DHCP Server . . . . . . . . . . . : 192.168.1.11
(There will be more data, but these are the crucial items.)
Record the DHCP Enabled setting, the IP address, and the DHCP Server (just in case you have more than one) for each machine.
Chances are that one of the following is true:
1) You have more than one DHCP server. Disable DHCP on the renegade device.
2) You have manually assigned an address in the DHCP range. Modify your DHCP server settings to either reserve the address or shrink the address pool size to avoid the duplicate reservation.
