I've installed Windows 8 Preview and Visual Studio 11 Preview. After I create a new Windows project and try to build VS, you need .net framework 4.5 while .NET Framework 4.5 is already installed!
Using the Visual Studio 11 Developer Preview means this error message is expected.
You need to switch to Visual Studio 11 Beta,
http://www.microsoft.com/visualstudio/11/en-us
