That's most likely the problem.
Do you have a digital with wired probe end you could use?
Ir thermometers rely on something called emissivity. Different objects (surfaces) have different emissivity. Most IR thermometers come precalibrated to a certain emissivity, and anything that falls outside of that range will not be read accurately. Unless you bought an IR thermometer with adjustable emissivity, you will not be able to really compensate for a surface that falls outside of it's calibration.
However, probe's don't have that problem, so I'd recommend doing a bit of a test with a probe on the two surfaces and see what they read. Then you'll know two things. What the actual temperature of both surfaces is, and which surface is the one that isn't compatible with your IR thermometer.
-Brandon
