during installation I get this error and then the app does a roll-back.
I am on a 64bit Win8 PC.
There are a number of potential problems here. If you are installing from a downloaded version of Rhino, then it is probable that the installer did not fully download and you should try to download again:
It is also possible that Windows update has not completed its download. You will want to make sure the windows 8 update is complete:
See if any of these help the install.
Here is our list of known installer issues: http://wiki.mcneel.com/rhino/installproblems