"WindowsUpdate_00000646" "WindowsUpdate_dt000"

You have to turn off UAC. After you turned it off, you should be able to install the updates without any problems. Go in Control Panel/User Accounts/Turn User Account Control on or off (you'll be turning it off at this point) Restart your computer. Once Windows is back up, install the updates. No problem. Once you're done installing, turn UAC back on. This is simpler. You can do this in Windows Security Update.