Hi FrazerA,
I have done some additional research and found others experiencing issues with installing. Here is an example > Problems installing.
The common solution seems to be creating a new administrator account and doing the install there. The individual from the thread above had to do it through safe mode. It seems to me this is an issue with the operating system.
You can also use Scannow to Repair Protected Windows Operating System Files. < Click here for instructions.
Keep me posted.