That means there is another Device somewhere if taking the IP assigned by
your Router or whatever server or Network device (DHCP) you are using to
Assign the IP.
It could be a printer, it could be another PC!.
Does your network assign Automatic IP address to your Laptop or Static IP?.
Does your Wireless secured by Encryption Key ( WPA,WEP) or any kind of
authentication to log only the real user not an intruder?.
HTH.
Let us know.
Regs,
nass