Happen to us one night also, no AGS system. Could have been a couple of things, a bug make contact in the slot on the generator would plug into an AGS, water in the AGS port. Ours did it only one time in 5 years. dealer told us we had a AGS system and that is why it started. LOL nothing pluged into the AGS port. Needless to say, we don't use that dealer any more.
2011: 54 days, 2012: 218 days, 2013: 175 days, 2014: 196 days
2015: 188 days, 2016: 72 days,
2009 Berkshire, 390QS, and toad