Immobiliser malfunction

[kjadebess]

I have a Ford grand cmax 2011 and I recently took it to the dealership for repair after it stopped recognising my key fob and the alarm went off.

The car also completely died and after towing it  they diagnosed a faulty receiver and alternator and replaced both. 

I have had it back 10 days and all seemed fine until today when I got a message saying immobiliser malfunction service now. The car still started and drove home, I could lock it with the fob upon exiting.

The only thing I can think of is i was sat with the car unlocked at school waiting, locked the car and came back after collection my son to see the back window was slightly down. I turned the car on and there was the message.

 

Any ideas?