There have been some changes to the WMI management interfaces in the release candidate of Hyper-V from the previous beta release.  While there have been no changes to the model, a number of the strings used in different places have been "cleaned up" to provide more "human friendly" values.  For instance, in this script I check for a caption value of "Microsoft Virtual Computer System".  The the release candidate build this is now a much simpler "Virtual Machine".

So if you have a script / program that you created with the beta and you are seeing issues with the release candidate - you should check the values that you are comparing against to ensure that they have not changed.

Cheers,
Ben