You mentioned that you are reinstalling the software, have you tried uninstalling the previous version? Not sure what's causing the error that you are seeing. I did a quick google search and found the following thread - I don't think it is related to what you are trying to do and hence my previous email about contacting TAC for assistance.
Sometimes windows server registry gets a little corrupted. The rights on the registry itself change be changed using regedt32.exe If you open the key you are having issues with, traverse down to that key and right click on the folder. Check permissions on the key or add your administrator account and try again.
Also - you may be able to just delete the key manually, then reboot, and reinstall...
Maybe afterwards using a registry cleaner utility will help clean it up as well.
Configure Multicast Paging on the Cisco IP Phone 7800 Series or 8800 Series Multiplatform Phone
The Cisco IP Phone 7800 and 8800 Series Multiplatform Phones provide voice communication over an Internet Protocol (IP) network...
Add Call Park on a Cisco 7800 or 8800 Series Multiplatform Phone Key Expansion Module
Call park allows the user of the phone to put an incoming call on hold so that the call can be retrieved on another phone. A call is park...