This happened to me just recently. Not sure why. To resolve I disconnected the battery for 15 minutes reconnected and problem resolved.
your battery is dying or is dead
By using your key to unlock the door.
Click the link for detailed instructions.
All electrical systems require voltage to operate, normally 11.5-12v, computers wont function properly below that.
Stick the key in the door lock and turn.
By sticking your key in the door lock and turning.
BMW's have auto-locks a little different from other cars, if your battery is dead, the doors won't open. To change the battery, you need to open the trunk, this is where the battery is located. You will see a panel with some screws, you need to remove that and underneath is the battery.
your battery is going dead
Use your key manuel like the old days. Kurt
Your battery is dead or you need to check the ignition switch.
Remove the rear seat.
use key to manually unlock. manual unlock will not work.