You must use the Role Management Tool to install or configure Microsoft .NET Framework 3.5

When trying to Install SQL Server 2008 on a Windows Server 2008 R2 machine, you get the following error:


This error happens because Windows 2008 R2 ships with .NET 3.5.1 Framework. To install you need to enable the feature via Server Manager.


This error will also happen with other Microsoft products that require .NET Framework as a Pre-Requisite such as Visual Studio 2008.