Newly installed this generator (purchased 7/3, installers finished yesterday 8/19). Activation code was mis-entered and now control panel states 'not activated'. Disconnected power at meter, battery and disconnected/reconnected all the terminal plugs we could reach/see on the underside of the controller.  Still refuses to let any further data be entered other than LP fuel and date/time before slipping back to the 'not activated' state.  We can run the unit manually, but automatic operation is not enabled.

Is there some other kind of sequence for starting over entering the activation code?

I have not had to try to re-enter, you did what I would have done by killing all power to the control. You should call Generac tech support if your installer is certified or customer support.
Ron Goldstein Rongold
I saw this on YouTube the other day, but it sounds like you did something similar with no success. It ends abruptly, but you'll get the drift of what he did.