Nissan Liberty

I have a Nissan Liberty 2001 (cvt gear box) which runs well when the engine is cold. When the engine heats up, the car stops changing all its gear and will loose power and have high revs. I took the vehicle for a scan and the error recorded reads P1720 V/SP SEN (A/T OUT). I have looked up this problem code but is not listed. Kindy explain what this code means, how can it be fixed and where can I get the spares if any are required.