Unable to install .net 3.5 on Windows server 2012

Solution 1:

This behavior can also be caused by a system administrator who configures the computer to use Windows Server Update Services (WSUS) instead of the Microsoft Windows Update server for servicing.

http://support.microsoft.com/kb/2734782

This worked for me. Windows has to download the 3.5 installation files, but the server is configured not to use Windows Update (common for managed servers), but WSUS. The above article describes how to fix this. In a nutshell:

1. Start the Local Group Policy Editor or Group Policy Management Console (WIN+R and type gpedit.msc).
2. Expand Computer Configuration, expand Administrative Templates, and then select System.
3. Open the Specify settings for optional component installation and component repair Group Policy setting, and then select Enabled.

4. Select the Contact Windows Update directly to download repair content instead of Windows Server Update Services (WSUS) checkbox.

5. Make sure Windows Updates Service is set to Manual or Automatic to apply this fix. Our default images are set to disabled, and the issue continued until that seemingly obvious change was made.

Solution 2:

Step 1: Uninstall any of these updates in: Control Panel -> Uninstall a Program -> View Installed Updates.

• KB2966826
• KB2966827
• KB2966828

Step 2: Then, retry installing the feature using the GUI (Server Manager), command line (dism), or PowerShell (Install-WindowsFeature)

Additional information on enabling features

Method 1: Using GUI - Server Manager

Server Manager -> Add Roles and Features -> Role-based or feature-based installation -> Select Server -> Features -> .NET Framework 3.5 Features

Method 2: Using Command Line - dism

dism : Using local installation media/Windows update/WSUS

dism /online /enable-feature /featurename:NetFx3 /all

DISM: With a local 'Alternate Source'

dism /online /enable-feature /featureName:NetFx3 /all /limitAccess /source:drive_letter:\sources\sxs

Please replace drive_letter with the drive letter of your local drive where the installation files reside

DISM: With a remote 'Alternate Source'

dism /online /enable-feature /featurename:netfx3 /all /LimitAccess /source:\\share_name\sources\sxs

Please replace share_name with the the UNC of the shared location where the installation files reside

Method 3: Using PowerShell

PowerShell: Using local installation media/Windows update/WSUS

Install-WindowsFeature –name NET-Framework-Core

PowerShell: With a local 'Alternate Source'

Install-WindowsFeature –name NET-Framework-Core –source x:\sources\sxs /source:drive_letter:\sources\sxs

Please replace drive_letter with the drive letter of your local drive where the installation files reside

PowerShell: With a remote 'Alternate Source'

Install-WindowsFeature –name NET-Framework-Core –source \\share_name\sources\sxs

Please replace share_name with the the UNC of the shared location where the installation files reside

Helpful Resources:

http://www.askvg.com/fix-0x800f0906-and-0x800f081f-error-messages-while-installing-net-framework-3-5-in-windows-8/

http://blogs.technet.com/b/askcore/archive/2012/05/14/windows-8-and-net-framework-3-5.aspx