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Enabling .NET Framework 3.5 fails with 0x800F081F

Troubleshooting guideSources checked: 2026-09-055 stepsFaultNote editorial team

What to do first

For 0x800F081F, check that the .NET 3.5 source matches the Windows version. On 26H1 and later, use the dedicated installer instead of Windows Features.

This is a general troubleshooting guide, not an announcement of a current outage.

Affected products and symptoms

Product
Windows 11 / .NET Framework 3.5
Versions and conditions
Windows 11 25H2 and earlier. Windows 11 26H1 (build 28000) and later use a standalone installation method and are outside this scope
Error codes and identifiers
0x800F081FNetFx3

Symptoms

  • .NET Framework 3.5 cannot be enabled in Windows Features
  • DISM reports that source files cannot be found

Causes and conditions

This occurs when the alternate source lacks the required files, read access is unavailable, or the installation media does not match the running Windows version.

Before you start

  • Record the version and OS build using winver
  • On an organization-managed PC, ask the administrator how features should be added
  • Prepare official Microsoft media matching the Windows version, language, and architecture

Precautions

  • Do not mix sources\sxs from different Windows versions
  • Do not use the old DISM procedure on 26H1 or later
  • Do not use .NET packages distributed by third parties

Tools and official pages used in this guide

Windows 11 / .NET Framework 3.5 troubleshooting sequence: Determine whether this is 26H1; Try the normal feature installation once; Check for a matching source; Enable NetFx3 using elevated DISM; Check the feature state
Procedure overview created by FaultNote. Read the precautions and full instructions before changing settings. Read the full steps

Step-by-step instructions

  1. 01

    Determine whether this is 26H1

    #

    Press Windows key+R to open Run, type winver, and press Enter. Record the version and OS build shown. For Windows 11 26H1 (build 28000), use the dedicated installer below and do not run the NetFx3/DISM procedures in steps 2-4.

    On 26H1, save DotNet35Setup.exe from the official download below, run it, and follow Microsoft's installation screens. After it finishes, launch the affected app to check. This file is only for the specified Windows version. On 25H2 or earlier, do not download it; proceed to step 2.

    Official links for this step

    Check before continuing

    On 26H1, install using the dedicated installer, check the affected app, and finish. On 25H2 or earlier, proceed to step 2.

  2. 02

    Try the normal feature installation once

    #

    On 25H2 or earlier, open Turn Windows features on or off from Start and select .NET Framework 3.5 (includes .NET 2.0 and 3.0). If it can be obtained from Windows Update, complete the process and restart.

    After selecting the checkbox, click OK. If prompted to obtain additional files, choose to download them from Windows Update. If this succeeds, restart and check the affected app; there is no need to additionally run the source-specification procedure.

  3. 03

    Check for a matching source

    #

    For 0x800F081F, mount official media matching the running Windows version, build, language, and architecture. In File Explorer, check the assigned drive letter and confirm that the sources\sxs folder is readable.

    Right-click the ISO in File Explorer and select Mount. Note the letter of the DVD drive added under This PC. If you do not have media matching your current Windows installation, do not substitute the latest ISO. On a managed PC, ask the administrator for media for the relevant build.

    Official links for this step

  4. 04

    Enable NetFx3 using elevated DISM

    #

    Open Terminal (Admin), replace D: with the actual media drive letter, and run the command. Wait for "The operation completed successfully."

    When the command finishes, check for "The operation completed successfully," a restart request, or an error code. If it fails, do not repeat the same operation; save the displayed code and C:\Windows\Logs\DISM\dism.log.

    Press Windows key+X and select Terminal (Admin). Replace only D: in the example below with the actual DVD drive letter, then press Enter. /LimitAccess specifies using the supplied media without contacting Windows Update, so do not try to fix a media-mismatch error solely by changing the internet connection.

    Command or path
    DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /Source:D:\sources\sxs /LimitAccess
  5. 05

    Check the feature state

    #

    Reopen Windows Features, confirm that .NET Framework 3.5 is enabled, and start the app that needed it. If 0x800F081F recurs, recheck the source version and read permissions.

Check the result

  • DISM completes successfully
  • .NET Framework 3.5 is enabled in Windows Features
  • The affected app starts without reporting that .NET is missing

If the problem continues

  • On an organization-managed device, ask the administrator for a compatible Features on Demand source or deployment method
  • If the media does not match, stop and obtain the correct version from Microsoft officially

Scope of this guide

Troubleshooting guide — Enable NetFx3 through the appropriate installation method so the legacy app that needs it can start.

Frequently asked questions

Should I run a general DISM repair first for 0x800F081F?

In this case, check for a mismatched alternate .NET 3.5 source first. This serves a different purpose from a general image repair.

Can I also install through Windows Features on Windows 11 26H1?

No. Starting with build 28000, use Microsoft's standalone installer dedicated to that Windows version.

Official sources and dates

Source publication or resolution date: Not specified. Sources checked: 2026-09-05. The check date is not the date the problem first occurred. Interface labels can vary between versions and display languages.

Related troubleshooting guides

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