E46 engine immobilized - key fob not recognized

I have a 2006 325 xiT. For no apparent reason, when the remote key fob is inserted, the car's software-module seems to not recognize the key as the vehicle's key and immobilizes the car. Same result with the 2nd key; not a dead battery in key fob problem. Both key fobs do open and lock the car. Symptoms: Steering column does not unlock (4 wheels remain locked); no interior lights; radio works ONLY if key fob is inserted. Battery is fully charged. Three weeks ago, the fuse controlling the cigarette lighter/auxiliary outlets had to be replaced. (Perhaps not related to instant problem??? mere coincidence?) Is there some immobilizer module or software responsible for this? Has anyone else experienced problem? Is this a known problem? Thanks very much. Ambrose24