After I installed Apple's recently released SMC Firmware Update on my MacBook Pro 2.0GHz it appeared to break Jonathan Pepin's CoreDuoTemp v0.6 and Dr. Marcel Bresink's Hardware Monitor 3.6 CPU temperature monitoring utilities.
After further research it appears that both CPU temperature utilities can be made to work again.
Pepin told me to trash the preference file "CoreDuoTemp.plist" and reboot. The preference file is located in:
Computer > Library > Preferences > CoreDuoTemp.plist
However doing this yielded the same error message that I received before. What fixed it for me was installing an updated version of CDT (v0.61). One small bug in the new CDT 0.61 is that it asks me to "download the latest free version" (even thought I already have it) at every launch. Probably just a small bug in the version code.
Somewhere along the line the weird "disconnected" error that I was getting from Dr. Marcel Bresink's Hardware Monitor 3.6 also went away, so I'm now able to monitor my MBP CPU temperature in both applications.
CoreDuoTemp relies on InCrew's SpeedIt kernel extension to get its information which is apparently broken by the SMC Firmware update.