I was trying to install PowerShell 2.0 and kept getting an error part way through that simply told me that access was denied while installing the Windows Management Framework Core. The installation was then rolled back. I tried a few times, with local and domain administrator accounts but to no avail. The following event was logged each time in the system event log:
After some poking around I found that the local Administrators group did not not have Full Control of the registry key HKLMSoftwareMicrosoftWindows NTCurrentVersionSvchost to which it was trying to write.
Just thought I'd share this in case anyone else encountered it.