Windows 10 – Unable To Install .NET Framework 3.5

Scenario:

  • You have Windows 10.
  • You need to install .NET Framework 3.5 which is not installed by default.
  • When you try and add the .NET 3.5 feature via Control Panel, it sits there for an age and then produces Error: 0x800F081F indicating it cannot locate the source files .
    OR
  • When you try to add the .NET 3.5 feature, it sits there for an age and produces Error: 0x800F0906 indicating it cannot download the source files.

I have now come across this issue on 4 separate Windows 10 installs. We need .NET Framework 3.5 for a business application to operate so it is vital to get it installed.

Having ‘Googled’ the subject, the issue would also appear to affect Windows 8.1 but personally, I’ve had no experience of it until Windows 10. A number of the solutions indicated an issue with Windows Server Update Services and to make edits to the Group Policy for the affected machine. However, we don’t use WSUS and one of the systems has Windows 10 Home installed, so Group Policy is a red herring.

A number of other posts solve the problem via a command line offline install from the original installation media.

I’ve had 100% success using the command line method but most of the posted solutions make some assumptions that actually make their instructions incorrect!

Lets have a look at the problem.

All of the solutions I found advise the use of the following command run from an elevated Command Prompt (search for CMD, Right Click, Run as Administrator):

dism /online/enable-feature /featurename:netfx3 /all /source:D:\sources\sxs /limitaccess

The letter ‘D’ after ‘source’ is the drive letter assigned to your Windows 10 installation media so may need to be changed. If you issue this command, you’ll end up with the following error:

DSIM error installing .net 3.5 on Windows 10.

You’ll note that the error number is actually the same as one of the symptoms to the initial problem, so initially you think it’s back to the drawing board. Not so!

All of the Windows 10 installation media (both USB Key and DVD) that I have come across contains both 32bit and 64bit install files. The command line error above is simply being produced because whoever initially authored the solution (which appears to have been copied verbatim by numerous posters) either had a single architecture install or has just re-hashed instructions from another version of Windows.

To prove my point, lets take a look at the folder structure of the Windows 10 USB Key:

Windows 10 USB Key Folder Structure

You’ll see that there are separate x86 (32bit) and x64 folders, so we need to edit the command line accordingly.

First of all you need to determine which Windows version you have installed. To do this, perform the following steps:

  • Right Click on the Start Button
  • Select ‘System’

You’ll get the following window containing the information you need:

Capture1

So, all you need to do is insert either x86\ or x64\ into the command line (after the D:\) depending on your version. For the (more common) 64bit version the command looks like this:

Dism /online/enable-feature /featurename:netfx3 /all /source:D:\x64\sources\sxs /limitaccess

Hit enter and after a short wait, the problem should be solved:

Correct path to install .NET 3.5 via DISM command line

Of course, there may be other scenarios out there that prevents this from working but as I have said, this has (so far) produced a 100% success rate.

Hopefully Microsoft will correct this rather annoying issue in a future update!

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