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Oblivion, Fallout: New Vegas and other apps crash after Windows 11 KB5124010 (msmpeg2ac3dec.dll)

Last verified October 2026Tested against KB5124010 (22 September 2026, optional preview) - the originating update, Windows 11 24H2, OS Build 26100.9550 and later, Windows 11 25H2, OS Build 26200.9550 and later, Windows 11 26H2, OS Build 26300.9550 and later, Sep2026LoadingCrashFix v0.2.0 (30 September 2026), Reported titles: Oblivion, Fallout 3, Fallout: New Vegas, SimCity 4Well documented

If a game or an older application started closing itself after a late-September 2026 Windows update, open Event Viewer and look at the faulting module. If it is msmpeg2ac3dec.dll, usually with exception code 0xc0000602, this is the AC-3 (Dolby Digital) decoder that KB5124010 broke - Microsoft confirmed it on 2 October 2026 and has not shipped a fix. KB5124010 is an optional preview update with no security content, so removing it costs you nothing. For Oblivion, Fallout 3 and Fallout: New Vegas there is a community script-extender plugin that makes Windows skip the broken decoder without touching game or system files.

Start here

  1. Confirm it is the audio decoder and not one of the update's other problems
  2. If you have not installed KB5124010 yet, leave it alone

Microsoft's own entry for this issue says only that applications which need AC-3 decoding "might close unexpectedly" and that a resolution will come in a future update. It does not tell you how to recognise the crash, which component fails, or what to do in the meantime. That information exists, but it is spread across a GitHub project, a German Windows blog and a two-year-old codec support page. This page puts it in one place.

Symptoms

  • An application or game closes with no error message, or fails to launch at all
  • Oblivion, Fallout 3 and Fallout: New Vegas crash right after the main menu, just before the loading screen appears
  • The application runs normally until something plays audio - background music, a ringtone, a cutscene
  • Windows Event Viewer logs the crash with faulting module msmpeg2ac3dec.dll, usually exception code 0xc0000602
  • Nothing changed on the machine except a Windows update on or after 22 September 2026
  • The PC is on OS build 26100.9550 (24H2), 26200.9550 (25H2) or 26300.9550 (26H2) or later
  • Another PC on the same Windows version is unaffected

Why this happens

KB5124010 shipped a broken AC-3 (Dolby Digital) audio decoder

Microsoft confirmed on 2 October 2026 that after installing the updates released 22 September 2026 (KB5124010) and later, some applications which require the decoding of AC-3 audio might close unexpectedly. Microsoft's own description matches what people are seeing: the application can fail to launch, or close without warning, or work normally until a feature such as playing music is used. The entry lists games, media players and productivity applications as possible casualties, and says the component involved is the one legacy applications use when they rely on Windows to decode audio rather than shipping their own decoder. The file that actually faults is msmpeg2ac3dec.dll, Microsoft's MPEG-2 and AC-3 audio decoder - Microsoft does not name it, but both the community plugin built for this and a reader report from 30 September identify it.

Confirm it is the audio decoder and not one of the update's other problems · If you have not installed KB5124010 yet, leave it alone · Remove KB5124010

The application does not have to use Dolby Digital for this to hit it

This is the part that makes the crash hard to recognise. According to the author of the community fix, the Bethesda games affected do not themselves use this decoder - but Windows tries to initialise it whenever the music changes, and on the second attempt it fails and takes the game down with it. That is why the crash lands at a consistent moment, just after the main menu, rather than when you load a Dolby Digital file. The reader who reported the problem to Born's Tech and Windows World saw the same library fault while MP3 files were playing, and an innovaphone myApps softphone crashing as it tried to play an MP3 ringtone for an incoming call. So "I never play Dolby Digital audio" does not rule this out.

Confirm it is the audio decoder and not one of the update's other problems · Oblivion, Fallout 3 or Fallout: New Vegas: install the community loading-crash plugin · Install LAV Filters so a different decoder handles the audio

Why an identical PC next to yours may be fine

Whether the crashing component is on the machine at all varies. Microsoft removed the AC-3 codec from Windows starting with Windows 11 version 24H2, but a PC that was upgraded to 24H2 from an earlier version of Windows keeps it, and many device manufacturers pre-install one. Microsoft has not said this is what decides who is affected, so treat it as context rather than a diagnosis: it is simply the reason two PCs on the same build can differ, and the reason this is reported mostly by people running older software on machines that have been upgraded rather than clean-installed.

Confirm it is the audio decoder and not one of the update's other problems

Fixes

Confirm it is the audio decoder and not one of the update's other problems

about 5 min

Several unrelated faults arrived with the same update, so check the faulting module before you change anything.

Applies to: Windows 11 24H2, 25H2 and 26H2

  1. Press Win+R and run winver. Note the OS build - this issue starts at 26100.9550 on 24H2, 26200.9550 on 25H2 and 26300.9550 on 26H2.
    winver
  2. Check whether KB5124010 is installed: Settings > Windows Update > Update history.
  3. Press Win+R and run eventvwr, then open Windows Logs > Application and find the Error logged at the moment the application closed.
    eventvwr
  4. Read the faulting module name. msmpeg2ac3dec.dll, usually with exception code 0xc0000602, means this article is your problem. If it names the application's own executable, an anti-cheat driver or a graphics DLL instead, you are looking at something else.

Confirmed by the vendor.

Source: Microsoft, Microsoft, Naragorn (GitHub), Born's Tech and Windows World (Gunter Born)

If you have not installed KB5124010 yet, leave it alone

about 2 min

It is an optional preview update with no security content, so declining it while Microsoft works on a fix costs you nothing.

Applies to: Windows 11 24H2, 25H2 and 26H2 that have not yet installed KB5124010

  1. Open Settings > Windows Update. If KB5124010 appears as an optional update, do not install it.
  2. Keep installing the monthly security updates. KB5124010 is a non-security preview release, so skipping it does not leave you unpatched - September's security content shipped in KB5124008 and in the 14 September out-of-band update KB5129195.
  3. Watch Microsoft's Windows release health page for this issue to move from Confirmed to Resolved before taking the next preview update.

Confirmed by the vendor.

Source: Microsoft, Microsoft

Oblivion, Fallout 3 or Fallout: New Vegas: install the community loading-crash plugin

Check before applyingabout 10 min

It tells Windows to skip the broken decoder for that one game, so music still plays and nothing on the system changes.

Applies to: The Elder Scrolls IV: Oblivion (xOBSE) - tested working, Fallout: New Vegas (xNVSE) - tested working, Fallout 3 (FOSE) - untested by the author

Before you do this

This is a third-party plugin first published on 30 September 2026, not a fix from Microsoft or Bethesda. It needs the game's script extender, it is only as trustworthy as its author, and Fallout 3 support is untested by the author's own admission. Read the repository before you install it. To remove it, delete the plugin DLL from the script extender's plugins folder - the author states it leaves game and system files untouched.

  1. Install the script extender your game needs: xOBSE for Oblivion, xNVSE for Fallout: New Vegas, FOSE for Fallout 3.
  2. Download the zip for your game from the project's GitHub releases page. v0.2.0 covers all three games - the same fix and the same DLL, packaged per game.
  3. Install it with your mod manager, or copy the contents into the game's Data folder so the DLL lands in the script extender's plugins directory.
  4. Launch the game through the script extender and check that it gets past the main menu into the loading screen.

Reported to work by one user; not confirmed by the vendor.

Source: Naragorn (GitHub), Naragorn (GitHub)

Install LAV Filters so a different decoder handles the audio

Check before applyingabout 10 min

LAV Filters registers its decoders at high merit, so DirectShow applications use them instead of the Microsoft decoder that is crashing.

Applies to: DirectShow applications: older games, media players, softphone clients

Before you do this

This changes audio and video decoding for every DirectShow application on the PC, not just the one that is crashing, and it is one person's tested report rather than a vendor-endorsed fix. It is reversible by uninstalling LAV Filters, but if you already maintain a deliberate codec setup, expect LAV's high-merit registration to take precedence over it.

  1. Download LAV Filters from its official GitHub repository, maintained by Nevcairiel, rather than from a codec-pack mirror.
  2. Install it with the default settings. The reader who tested this against the KB5124010 crash reported that no special configuration was needed.
  3. Restart the application that was crashing and play the audio that triggered it.

Reported to work by one user; not confirmed by the vendor.

Source: Nevcairiel (GitHub), Born's Tech and Windows World (Gunter Born)

Remove KB5124010

Check before applyingabout 15 min

It is the originating update and carries no security fixes, so taking it off puts the working decoder back.

Applies to: Windows 11 24H2, 25H2 and 26H2 with KB5124010 installed

Before you do this

Do not use this route to remove September's security updates - KB5124008 and the 14 September out-of-band update KB5129195 are separate releases and should stay installed. Removing KB5124010 is reversible, but the author of the community fix notes that Windows may reinstall the update later, so treat this as temporary rather than settled.

  1. Open Settings > Windows Update > Update history.
  2. Under Related settings, select Uninstall updates.
  3. Select KB5124010 in the list, choose Uninstall, and restart when prompted.
  4. Run winver afterwards - the build should be back below 26100.9550, 26200.9550 or 26300.9550 for your Windows version.
    winver
  5. If KB5124010 is not in the list, it cannot be removed this way; Microsoft notes that some updates cannot be uninstalled.

Reported to work by 2 users; not confirmed by the vendor.

Source: Microsoft, Microsoft, Microsoft, Naragorn (GitHub)

Known issues

  • Microsoft lists this as Confirmed on Windows 11 24H2, 25H2 and 26H2, originating in KB5124010, and says a resolution will come in a future Windows update. As of 3 October 2026 no fix has shipped and Microsoft publishes no workaround of its own.

    Affects Windows 11 24H2, OS Build 26100.9550 and later, Windows 11 25H2, OS Build 26200.9550 and later, Windows 11 26H2, OS Build 26300.9550 and later · Status: open

  • Every workaround on this page comes from the community, not from Microsoft or the affected software's publishers. The script-extender plugin covers three Bethesda titles only, and the LAV Filters route rests on a single tested report.

    Affects Sep2026LoadingCrashFix v0.2.0 · Status: workaround only

If none of this worked

KB5124010 broke more than one thing, and the fixes do not overlap. If a game with anti-cheat closes 20 to 30 seconds after launch rather than at the main menu, and Event Viewer does not name msmpeg2ac3dec.dll, that is the separate and still unacknowledged crash pattern covered in our article on anti-cheat games crashing after KB5124010. If a USB headset or speaker shows "This device cannot start (Code 10)" or produces no sound, that is the USB Audio Class 1.0 problem from KB5124008 instead. If a virtual desktop shows a black screen after sign-in, that is a third, separate entry on Microsoft's release health page with its own Known Issue Rollback. And if the faulting module is the application's own executable, nothing here applies - start from the application's crash logs.

Common questions

Is this the same problem as Battlefield 6 crashing after KB5124010?
Probably not. Those reports describe games with anti-cheat closing roughly 20 to 30 seconds after launch, and Microsoft has not acknowledged them. This issue is vendor-confirmed, crashes at a different moment - right after the main menu, or whenever audio starts - and leaves a specific signature in Event Viewer: msmpeg2ac3dec.dll with exception code 0xc0000602. Check the faulting module before assuming either. Note that Fallout: New Vegas has been named in both sets of reports, and for that title the decoder fault is the better-evidenced explanation because it has a named faulting module and a tested fix.
Will removing KB5124010 leave me missing security fixes?
No. Microsoft's own page for KB5124010 describes it as an optional preview, non-security update released on 22 September 2026. September's security content shipped separately in KB5124008 on 8 September and in the out-of-band update KB5129195 on 14 September, and neither is removed by uninstalling KB5124010.
Why is another PC on the same Windows build not affected?
Whether the decoder is present at all differs between machines. Microsoft removed the AC-3 codec from Windows beginning with Windows 11 version 24H2, but a PC upgraded to 24H2 from an earlier Windows version retains it, and many manufacturers pre-install one. Microsoft has not stated that this is what determines who hits the crash, so treat it as the likely reason for the variation rather than a confirmed rule.
Has Microsoft shipped a fix yet?
Not as of 3 October 2026. The issue was opened on 2 October 2026 and is listed as Confirmed on the Windows 11 24H2, 25H2 and 26H2 release health pages, with Microsoft saying only that it is working on a resolution for a future Windows update.
I do not play Dolby Digital files, so can this still be my crash?
Yes. The author of the community plugin reports that the affected games never call the decoder themselves - Windows initialises it when the music changes and it fails on the second attempt. A reader report also describes the same library faulting while ordinary MP3 files were playing, and a softphone crashing on an MP3 ringtone. The audio format you deliberately use is not a reliable way to rule this out.

Did this fix work?

If a step is wrong, outdated, or did not help, telling us is the fastest way to get it corrected. Reports are reviewed before new articles.

Report a problem with this page

Related problems

Sources

  • Windows 11, version 25H2 known issues and notificationsOfficial

    Microsoft · Release notes · checked Oct 3, 2026

    • Microsoft lists "Applications which require AC-3 audio decoding might close unexpectedly" with status Confirmed, opened 2 October 2026
    • The issue originates in OS Build 26200.9550 (KB5124010), released 22 September 2026
    • Affected applications can fail to launch or close without warning, and in other cases work normally until a feature such as playing music is used
    • Affected applications may vary and can include games, media players and certain productivity applications
    • Microsoft says it is working on a resolution in a future Windows update and publishes no workaround for this issue
    • September's security update was KB5124008 and the out-of-band update released 14 September 2026 was KB5129195
  • Windows 11, version 26H2 known issues and notificationsOfficial

    Microsoft · Release notes · checked Oct 3, 2026

    • The same AC-3 audio decoding issue is listed for Windows 11 version 26H2 with originating OS Build 26300.9550 (KB5124010)
    • Affected platforms are Windows 11 version 26H2, version 25H2 and version 24H2, with no Server versions affected
  • KB5124010: Windows 11, version 24H2 and 25H2 updateOfficial

    Microsoft · Release notes · checked Oct 3, 2026

    • KB5124010 is an optional preview, non-security update released 22 September 2026
    • KB5124010 covers OS builds 26300.9550, 26200.9550 and 26100.9550
    • The update's own known-issues section states that applications which require AC-3 (Dolby Digital) audio decoding might fail to launch or close unexpectedly when certain audio features are used
  • Codecs in Media PlayerOfficial

    Microsoft · Documentation · checked Oct 3, 2026

    • Beginning with Windows 11, version 24H2, the AC-3 codec is no longer included with Windows
    • If you upgrade to Windows 11, version 24H2 from an earlier version of Windows, the AC-3 codec is retained
    • Many device manufacturers pre-install an AC-3 codec
    • Microsoft offers no AC-3 codec download of its own on this page
  • How to uninstall a Windows updateOfficial

    Microsoft · Support page · checked Oct 3, 2026

    • On Windows 11 the path to remove an update is Start > Settings > Windows Update > Update history > Uninstall updates, then select the update and choose Uninstall
    • Some updates cannot be uninstalled
  • Windows 11 24H2/25H2/26H2: Probleme mit Vorschau-Update KB5124010Reputable

    Born's Tech and Windows World (Gunter Born) · News · checked Oct 3, 2026

    • A reader reported by email on 30 September 2026, before Microsoft acknowledged the issue, that software crashes in msmpeg2ac3dec.dll when MP3 files are played
    • The same reader reported that older games including SimCity 4 and Fallout: New Vegas are affected
    • The same reader tested LAV Filters and reported that it resolves the problem with no special configuration, installed with default settings
    • An innovaphone myApps softphone client crashes when it tries to play an MP3 ringtone for an incoming call
  • Naragorn/Sep2026LoadingCrashFix: Fixes Oblivion crashing before the loading screen after Windows 11 update KB5124010Community report

    Naragorn (GitHub) · Reference · checked Oct 3, 2026

    • The affected games crash immediately after the main menu, before the loading screen appears, on Windows 11 systems that received KB5124010
    • The crash appears in Windows Event Viewer as exception code 0xc0000602 with the faulting module msmpeg2ac3dec.dll
    • The plugin works around the crash by instructing Windows to skip the broken decoder while the game runs, leaving game and system files untouched, with music still playing through the standard MP3 decoder
    • Oblivion requires xOBSE and Fallout: New Vegas requires xNVSE, both tested working; Fallout 3 requires FOSE and is untested
    • Per the plugin author, the games do not themselves use the decoder, but Windows attempts to initialise it whenever music changes and on the second attempt it fails and takes the game down
    • The author lists uninstalling KB5124010 as an alternative and notes the update may reinstall automatically
    • Installation is by mod manager or by copying the contents into the game's Data folder so the DLL lands in the script extender's plugins directory
  • Releases - Naragorn/Sep2026LoadingCrashFixCommunity report

    Naragorn (GitHub) · Reference · checked Oct 3, 2026

    • Version v0.1.0 was released on 30 September 2026 covering Oblivion
    • Version v0.2.0 was released later the same day and adds Fallout 3 and Fallout: New Vegas, described as the same fix and same DLL with a separate zip per game
  • Nevcairiel/LAVFilters: LAV Filters - ffmpeg based DirectShow Splitter and DecodersCommunity report

    Nevcairiel (GitHub) · Reference · checked Oct 3, 2026

    • LAV Filters is an FFmpeg-based set of DirectShow splitters and decoders, maintained by Nevcairiel and distributed through its GitHub repository
    • Its audio and video decoders register with high merit, so DirectShow applications prefer them over other installed decoders