Prism, I am trying to not go deep on the OP's issue. And it appears Doug is not either. As for folks running their generator, Yes but in many cases there is a shut off of the combining of the batteries so the generator will not show an "over voltage" issue to the alternator circuit.
The shoreline charging system is not "disabled" on the engine battery feed and can cause the alternator alarm.
Alternators are one of the simplest systems on an RV. Good connections and tight belts and they usually work or don't. A volt meter on the output lead will tell the story in seconds.
As suggested, I too have had brand new ones inop. However doing as suggested may save a lot of knuckles and back pain.