Strange IP mesage

It means that two devices are trying to use the same IP address on your router, do you have any other wireless devices apart from yours and your wife's computers?

 

Are your computers using DHCP or DHCP with Manual Address. Just unplug your router first. Reset your computers to use DHCP, then shut them down. Plug in your router again, and wait for it to load. Then turn your computers back on, it should correct the IP address solution. If it dosen't, set your settings to DHCP with manual address, and set the IP to something like 10.0.1.10, and your wifes using the same settings, but IP address 10.0.1.15.

Otherwise call/take your computer to Apple and have them walk you through it.

 

I get this too, on my home network. There are 4 computers that use it regularly, and 2 that occasionally use it. However, whether the 2 that are only sometimes present are there doesn't seem to make any difference.