personally i'd check the connections between the secs monitor and the loom first mate.
if the connection is dodgy/being broken, then it will flash this message up.

if the connection is good, and the car loom is in good condition, then its possible the sensor is on the way out.



Edit: unsure if it flashes this message if the sensor goes 'out of range' for the monitor?
simon will be along shortly to reveal all im sure!