I have a 1999 S500 and got a "valet key" from the dealer. I had never used this key until I tested it in preparation for a trip on the autotrain to Florida. A couple times it started the car, however, sometimes it wouldn't start the car. I found that where the mileage is displayed, an error notice came up when starting the car. Who can tell me what the story is on the "valet key"?