I got the FitBit Aria and had some trouble setting it up with my WiFi network. At first I was getting the "WIFI ERR" message from the scale. It turns out that if you have a relatively new cable box / wireless router from Comcast / Xfinity, it does not enable 802.11b by default. The way to fix this is explained here:
After I made the changes to the router configuration, the FitBit Aria worked.
I wasted a lot of time wondering why it was trying to connect to my neighbor's WiFi instead of mine. It was just because of 802.11b needing to be enabled.