why don't some WMI classes work?

You might need to rebuild your WMI registry.n

nHere is a good link for troubleshooting wmi.n

nhttp://blogs.technet.com/b/configmgrt...n

nAlso if you want to completely just rebuild wmi run the winmgmt /salvagerepository command.n

nThe above command performs a consistency check on the WMI repository, and if an inconsistency is detected, rebuilds the repository. The content of the inconsistent repository is merged into the rebuilt repository, if it can be read.