Currently on Windows Server 2008 R2, .NET Framework 3.5 SP1 comes as a feature in Server Manager. Since this is a feature of the operating system, Windows does not allow installation during normal program installation. This feature must be installed separate from the program.
Download the corresponding installation file
- Click the Start menu.
- Click All Programs.
- Highlight Administrative Tools and select Server Manager.
- In the Server Manager Interface, click Features.
- Select Add Features to display a list of possible features.
- In the Select Features interface, expand .NET Framework 3.5.1 Features.
- Check the box next to .NET Framework 3.5.1 and click Next.
- In the Confirm Installation Selections interface, review the selections and then click Install.
- Allow the installation process to complete and then click Close.