turn on ASP.NET 4.0

This and this has a good article on how to beat this error when running a web site in Visual Studio via IIS:

ASP.NET 4.0 has not been registered on the Web server. You need to manually configure your Web server for ASP.NET 4.0 in order for your site to run correctly, Press F1 for more details.

• Try to turn on everything when prepping IIS7 except for "IIS6 Management Console"
• Open a command prompt as an administrator and type:
  aspnet_regiis.exe -i
  ...at:
  C:\Windows\Microsoft.NET\Framework\v4.0.30319\