Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.
Unfortunately this indicates that your vehicle is in security/theft mode,this causes the no start issue.This can occur when the key signal fails internally with the key/remote with it needing replaced and programmed to your vehicle or when another component fails like the immobilizer itself that reads the key as I have seen before.
What you can try here to see if this works is try to lock and unlock the vehicle with the key or remote then see if it starts.If this was already attempted or is attempted with the same results this indicates one of the security components has failed on your vehicle.
Unfortunately what will need to be done from here because it is difficult to say for sure which component has failed without seeing and testing the vehicle,is to have a scan tool/computer that is fully compatible with your vehicle plugged into your vehicle to read out the fault codes to see what codes are set.Once this has been done any codes set need to be diagnosed to locate and repair the fault here.
I can say most common is the key itself failing needing replaced and programmed.The programming needs done by a dealer or authorized repair center that works on BMW vehicles.
If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.