Optimax 4 beeps then no start

[legallimits]

Appreciate the input. That chart is the same one that's in my service manual, and it means either water in the gas or oil. I've never had water in the gas, and the problem popped up when I stopped to put oil in the tank. So it's got to be oil. But it doesn't seem like low oil or a bad sensor would cause the engine to not start. Seems like it should still start but then beep at me. It could be a huge coincidence with some other kind of problem, but it doesn't seem like it.