Well it's a brand new Windows 7 x64 setup and after running the installer from Microsoft's website, I got this error.
To fix it, grab the latest version of the .NET framework from Microsoft's website. I downloaded 4.5 and it fixed the installer.
You can get the link to the latest version on the right hand side column.
So seriously, what the hell? It says during the installer that it'd install .NET for me! After the release of Windows 7, they've really dropped the ball on quality!