Error is coming in Windows server 2008 during installing Dot Net framework 3.5

During installing Dot Net framework in Windows Server 2008 the following error is coming. How to overcome from this problem?

Error:
Microsoft .NET Framework 3.5 Setup
You must use the Role Management Tool to install or configure Microsoft .NET Framework 3.5.
Answer:
During installing Microsoft .Net Framework 3.5 in windows server 2008, the following error may occur.

This error is coming because Windows 2008 R2 ships with the .NET 3.5.1 framework. You need to enable the feature from Server Manager. Use the following steps to resolve the problem…

1. Go to Start > Administrative Tools > Server Manager
2. Click on Features
3. Enable .NET 3.5.1 framework features