Gearbox Overheat

I have bought my first Range Rover P38 and have the GEARBOX OVERHEAT flashing away at me.
It would appear this is not actually the case as the gearbox has now been tested and is showing as running at the correct temperature. Also the warning appears as soon as you put the key in the ignition 1st thing in the morning.
Therefore i am lead to believe this is a faulty sensor??
Does anyone know where on the car i will find the sensor and what i can do to remidy the situation???

Cheers

Iain

Has the vehicle got a good strong battery, if the battery is a little tired you'll get gearbox warning messages appear

Thanks I will try that tonight.