Service Engine Soon Light comes on after filling up?

[2006BMWx5]

I have searched around and have seen a few post but if the experts can point me in the right direction...not looking forward to having to take the car to the dealer...(it is covered under CPO warranty but closest dealer is 1 1/2 hrs away)

Here is exactly what has happened twice now...

1st time... I filled the car up premium gas...from a gas station I use all of the time...the next day wifey starts car and the service engine soon light comes on (not service indicator) and stays on will not shut off, cut car off and restarted same thing...so check oil, fluids, gas cap...OK car seems to run fine. I have had it serviced about 3k miles ago too service indicator light is still good. Call BMW Dealership and ask them what it could be...lady I talked to said it could have to do with the gas but if the car ran fine see if the code goes off by itself. She said it could take driving it 7 - 10 times 15 miles or more? OK...wife drives the car and sure enough day 5 light shuts off...GREAT!

So a few days go by and yesterday the wife fills up the car at another gas station and today guess what the light comes back on... I asked her if the car did anything weird when it came on and she said it did not, put the gas cap on...YES. I am not sure if I should just see if the code goes off again or take it in...

Any and All help and suggestions are appreciated!