I had this same exact problem with my car a few weeks back.
I called BMW and they said it is most likely refueling with the car running. I might have done this a few days prior, but really don't remember.
They said to wait a week and if it is still there, make an appt for service.
After about 5 days it went out for a few hours. Came back on shortly after, stayed for a few days.
2 days ago the light went out and has been out ever since. Performance of the car has not changed at all during this entire thing.