Just bought a Brother HL-2270DW laser WiFi printer. I have a mac pro and an Airport Extreme. I followed the instructions but when I unplug the USB cable my Mac Pro says the printer is offline. If I plug the cable back in it works fine. I know the printer is setup and works on my WiFi because I can print from my iPad and iPhone. Even though my Mac Pro is connected to my Airport does it have to be on WiFi also?