Well, unless your 'Super-Cooling' there's a problem with the sensor. Have you tried to obvious checks?
1) Pull the CPU and make sure that the leads of the sensor aren't touching anything metalic.
2) Is there any contaimination between the leads which might be shorting it?
3) You would have had to bend the sensor slightly to mount the CPU...you didn't break or crack the leads did you?
4) Check the BACK SIDE of the motherboard. The sensor leads stick out farther than the rest of the circuitry does, perhaps its shorted on the back side? (I clipped mine flush with the board).
Hope this helps,
Ray