When Windows Server 2008 is installed and the IIS roles are enabled, it defaults to .Net 2.0.

If you want to run .Net 3.5.1 on the server you might think the process is as easy as just downloading the bits from Microsoft and running the installation process. No, it isn't. It still isn't hard, but it can be frustrating for someone who isn't familiar with the required process.

To enable .Net 3.5.1 on a Windows Server 2008 machine that already has the IIS role enabled...

To get started, from within Server Manager you need to select Features in the left-hand tree and then Add Features in the right-hand pane.

NOTE: I have the SMTP feature enabled on this test server but on your machine you likely won't see that listed.

On the next screen select the ".Net Framework 3.5.1 Features" option from the list.

As soon as you click that box, a pop-up window like the one below will be displayed.

Clicking "Add Required Features" will then install the necessary dependencies and files required to support .Net 3.5.1 on the server.