if you install .NET Framework 4
after installing IIS then everything gets registered properly. However, if you install .NET Framework 4
before installing IIS then you need to perform an extra step:
aspnet_regiis.exe -iru -enable
http://rockyprogress.wordpress.com/2011/09/06/iis-7-5-and-net-framework-4-installation-order-does-matter/