Must be something to do with the weather.
I have a 04' 645ci and never had a problem with it at all but yesterday started it up and had the same problem. Very rough idle with the same message displayed on the iDrive. I did not attempt to revv the engine, but just turned the car off and restarted it and nothing came up.
Since then I have started and run the car numerous times with no problems. Hoping its nothing serious...