Electronic fault-car wont start?

My renault megane 03 plate wont start, the key card clicks all the door windows but nothing, its saying electronic fault. Had 2 small children in the car, RAC came out and said it could be the immobiliser sometimes gets stuck. RAC disconnected the battery and when it was placed back on it started. I managed to get home but when I tried to start it-no go, this is crazy.