Every time I try to set up a new button rule, every time I get to the point where I'm telling it what a button should do I get an error screen.
Give the hub a reboot (from the "Settings" page, as you always should do for shutdowns or reboots) and it should fix itself. Seems to be an oddity some people have the first time after upgrading firmware.
OK, that's funny because I upgraded the firmware right before this. A reboot took care of the button controller issue. Thanks!