"Many of the issues I've seen lately with not connecting to WiFi involve a customer trying to connect to a WEP-based network. If the network uses WEP, there are many problems with the network, not the least of which being completely insecure and not supporting 802.11n - so you're stuck at 54mbps on your shiny new 300mbps router. :)
The WiFi board in the JuiceBox supports WEP, but only by tweaking some settings at a console - and because of the security & performance problems with WEP, it's a good opportunity to improve the security as well. You can force-enable WEP by going to the console tab in the "setup.com" page and entering "set wlan.security WEP" after having done "save & continue" on a previous failed connection attempt. However configuring the WiFi network for WPA2-AES is the best choice as that's the best way to get more performance and security out of the WiFi network."