Diagnosis
That's a classic sign of the firepot not getting enough airflow to light the pellets properly. The grill's trying to start but fails, so it throws a general error and shuts down for safety.
How to Fix It
First, make sure the grill is completely off and cooled down. Pull out the grates and the heat diffuser plate so you can see the firepot at the bottom. Vacuum out every single bit of ash and pellet dust from the firepot and the surrounding burn chamber. It doesn't take much debris to choke out the initial flame. After cleaning, do a fresh startup cycle with a small handful of pellets in the firepot to give it an easy start.
If That Didn't Work
Check the little metal rod that pokes into the firepot—that's the hot rod igniter. If it's covered in heavy carbon scale or looks damaged/broken, it might not be getting hot enough to light the pellets. You'll likely need to replace it, which is a common spare part.
Heads Up
Always do your startup cycle with the lid open. The grill needs that extra oxygen to get the initial fire going strong. Closing it too soon is a surefire way to get an 'err' message.