We ran into this message today while trying to install .NET Framework 3.5 on a Server 2008 R2 box. I know people are going to run into this, so I figured I’d share the answer that we found from Bryan:
“Windows 2008 R2 already ships with the .NET 3.5.1 framework so you just need to enable the feature from Server Manager.”
“So before installing the Visual Studio 2008, we enable the .NET 3.5.1 framework feature from the Add Features Wizard in Server Manager.”