2000 Jaguar XJ8 Traction, Gearbox Control Failure Message

I can be driving on the highway or parking lot and traction control message will appear with gearbox failure. The service light will show red. The engine goes into a engine fail safe mode which allows the car to stay on and move at an idyle speed. The service light show yellow then. The vehicle will not accelerate. This problem happen intermitently and it can be at anytime with no notice or pattern. The Jaguar Dealer can not find the problem. The vehicle have been serviced and the next day the problem appear on her way from work. We have turn the vehicle off when it goes into the fail safe mode and it then most of the time it resets after waiting five minute or cutting on and off couple of times the service light will turn off, then I know it will return to opperation ready. If the yellow warning light is on before the engine goes to fail safe mode and I stop the vehicle to place it in park, going through the gear, as I past through reverse the vehicle gears slam hard before going in park. What should I do to correct this problem? I have ask the dealer to replace the transmission filter and fluid and have one of his personnel to drive the vehicle a week to see if the problem is still there. Please help me!