Simplest thing try a restart of your machine.
Second Try the offline installers located at the bottom of the page listed under 'still having problems'
This may happen because of a certificate problem. The online installer uses the SHA256 certificate, which may not be compatible with a computer that is running Windows Vista SP2. If this is your setup, you can use the offline installer Carm01 links to and/or visit this Microsoft Support page to download an update for your operating system. See Microsoft Security Advisory 2880823 for more information.