Hi
I had the same problem on a W7 32 bit install. The three steps I took were
1. The two icacls command line changes
2. Giving the IIS account full control over the web site root
3. The same for the Temp directory in the user's AppData/Local folder.
Initially that didn't change anything, reboot required and then it all worked.
Can't see any reason why 64 bit would be different, but I'll find out in the next few days when I do the same thing for another machine with 64 bit installed!
Good Luck
Tim