The fault code description applies when cranking the generator. It's incomplete as it doesn't mention what the code means after it's been running for a while.
What I think it MAY be is dirty slip rings. Take a 1/2" X 12" long square stick and glue some sand paper on one end. Locate the air slots on the end of the generator and with a flashlight, locate the two slip rings. Start the engine and rest the sandpaper on each slip ring in turn as the engine spins. This cleans the slip rings and brings the resistance back down to normal range.
If it still stalls after running two minutes, then it's probably the voltage regulator.
Other causes for this symptom (but a different code than you're getting) is low oil level. Check that anyway...just to be sure.