[Mark McLeod]

As part of securing the integrity of the field network at the event the robot bridge gets it's security mode set to WPA and a unique random code generated for each team. That's one reason why the DS router is useless at competition (aside from the extra wireless network the FTA doesn't want broadcasting) and is why the robot won't respond to wireless when you get it back home.

When teams get their robots back home they need to connect (wired) to the robot bridge, browse to the bridge (10.xx.yy.1) and to the Basic -> Wireless setup page, and for Security Mode select "None".
P.S. I've attached a shot of what the screen looks like and you can see "Security Mode: None" at the bottom. This image is glommed from the Control System manual chapter 2.

Of course you can also use the security at home, but you'd have to turn it on for the DS router and you'd have to change the security code to a common random value (anything your heart desires) on both the DS router and the robot bridge. You'll find the masked field to enter a code under the WPA security setting.