Has anyone had this problem?  Transmission fail safe mode comes on and throws the car into third gear.  Message says braking is unsafe, and it can only be driven in "drive."  At the time the notice comes on there is a bold jerk and noise.  I am told that the car is putting itself into third gear.  The only way to get out of this is to stop in sometimes unsafe places and turn the ignition off.  This has happened to me seven times.  My auto has been at Century BMW in Greenville, SC for ten days with no diagnosis.  They have suggested that I start out by replacing the battery and alternator and see where that goes.  However, I don't feel comfortable replacing expensive parts to help them in their diagnosis.  They cannot guarantee that replacing the parts will fix the car.  The service manager has not returned my phone calls since our initial conversation after three or four requests.