TD5 Autobox problems

Hi,

The Autobox on my TD5 2000 this morning has just started flashing one of the red lights down the side of where you change gear, and the light is flashing next to Drive, If I change down from drive to 3,2 or 1, nothing happens and the red light continues flashing next to Drive and only stops flashing when you are either in park or reverse.

I changed the oil and screen filter about 15,000kms ago the car has done 140,000kms all ideas welcome.

Thanks in advance.