How to fix mso.dll missing or not found error in Windows?

mso.dll is the shared library that every Microsoft Office app loads, so an mso.dll error means Office itself, not Windows, is broken or blocked. When the app crashes, an add-in is the most common trigger; start it in Office Safe Mode. When it will not start, repair Office.

Facts checked on 16 October 2026. Steps written for Microsoft 365, Office 2024, 2021, 2019 and 2016 on Windows 11 (25H2 and 26H2) and Windows 10 22H2, read against Microsoft Support pages and Microsoft Q&A cases.

What the mso.dll error means and how it shows up

mso.dll is the Microsoft Office shared library. Word, Excel, Outlook, PowerPoint, Access and Publisher all load it for the ribbon, file dialogs, spelling, add-ins and other common parts. It belongs to Office, not to Windows, and it is not stored in System32.

Because every Office app depends on it, mso.dll is named in two quite different problems. Tell them apart first, because the fix is different.

What causes mso.dll errors, from the most common to the rare

Microsoft publishes no list of causes for mso.dll. The order below comes from Microsoft's advice for Office apps that crash or will not start and from the cases users posted on Microsoft Q&A. It is an order of likelihood, not a statistic.

mso.dll location: where the file is for each Office version

Crash reports name the full path in the line Faulting module path. Use it to see which Office the crash belongs to. The folder name carries the Office version number, not the year.

Do not copy mso.dll between these folders or between PCs. The file must match the build of the rest of Office, and only setup or repair keeps them in step. If the folder is empty or missing, Office is damaged and Fix 2 or Fix 6 rebuilds it.

How to fix the mso.dll error in Word, Excel and Outlook

Fix 1 and Fix 2 solve most cases. Fix 1 is for crashes, Fix 2 for a missing file and for crashes that Fix 1 did not explain. Fix 3 to Fix 6 deal with conflicts, settings and a broken installation. Fix 7 is a general Windows check for the rare case where other programs fail too.

Fix 1. Start the app in Office Safe Mode and turn off add-ins

5 to 15 minutesLow riskWord, Excel, Outlook or PowerPoint crashes and Event Viewer names mso.dll as the faulting module.

Microsoft says Office Safe Mode helps find an add-in or extension that causes a problem. Safe Mode skips add-ins and customizations, so if the crash stops there, something loaded into Office, not mso.dll itself, is the cause.

1. Close the Office app completely.
2. Press Win + R, type winword /safe for Word, excel /safe for Excel, outlook /safe for Outlook or powerpnt /safe for PowerPoint, and select OK.
3. Or hold Ctrl while you open the app's shortcut and select Yes when it asks about Safe Mode.
4. Do what made the app crash before: open the file, save, send the mail.
5. If there is no crash, close the app, start it normally and open File > Options > Add-ins.
6. At the bottom, set Manage to COM Add-ins and select Go.
7. Clear the check box of one add-in, select OK and test. Repeat until the crash stops.
8. Leave the guilty add-in off, then update or remove it.

For Outlook, test sending mail in outlook /safe. Users on Microsoft Q&A report that crashes when sending often come from mail add-ins, such as scanners and CRM connectors. Safe Mode does not save templates or preferences, so close it and start normally when you are done.

Fix 2. Repair Office with Quick Repair, then Online Repair

10 to 30 minutesLow riskMso.dll was not found, or every Office app crashes, or Safe Mode did not help.

Repair checks every Office file, mso.dll included, against your installed build and replaces damaged or missing ones. Microsoft notes it repairs the whole suite, even if only Word or Excel fails, and recommends Online Repair to make sure everything gets fixed.

1. Open Installed apps. Right-click the Start button and select Installed apps.
2. Find Microsoft 365 or Office. Find your Microsoft 365 or Office product in the list. If you have a standalone app such as Visio or Project, search for it by its own name.
3. Open the repair window. Select the three dots next to the product and select Modify.
4. Start with Quick Repair. In the repair window, select Quick Repair, then Repair. It is the faster option: it finds damaged files and replaces them.
5. Finish and test. Follow the instructions on the screen until the repair is done. Restart the PC if you are asked to, then open the app that had the problem.
6. Run Online Repair if the problem is still there. Open the same repair window again and select Online Repair, then Repair. Microsoft recommends this option to make sure everything gets fixed. It takes longer than Quick Repair.

These steps were written for Windows 11 25H2 and 26H2. The full page with the other versions and what each result means: How to repair Microsoft 365 or Office

• Click-to-Run Office (Microsoft 365, Office 2019 to 2024 for home): choose Quick Repair first. If the error comes back, choose Online Repair, which needs an internet connection and takes longer.
• MSI Office (volume editions of Office 2016 and older): the window is called Change your installation. Select Repair and Continue.
• Restart the PC when the repair asks, then open the app that failed.

Fix 3. Remove old Office plug-ins and change the installed Office features

15 minutesLow riskRepair finished, but Excel, Word or Outlook still crashes with mso.dll at the same action.

One user on Microsoft Q&A found that repair did not stop an Excel crash in mso.dll. Removing an old plug-in program and removing one Office feature (Publisher) did. Repair replaces files but leaves installed plug-ins and the chosen features alone.

1. Open Settings > Apps > Installed apps (Windows 10: Apps & features).
2. Look for programs that add to Office: PDF printers, toolbars, CRM or mail plug-ins, old conference tools.
3. Uninstall those you no longer use: Uninstall a program or app in Windows.
4. For MSI Office only: open Control Panel > Programs and Features, select Office and Change, then Add or Remove Features.
5. Set a feature you do not use, such as Publisher, to Not Available, select Continue and restart the PC.

Click-to-Run Office has no Add or Remove Features choice in this window. There, removing the plug-in programs is the part that applies.

Fix 4. Turn off compatibility mode for the Office app

5 minutesNo riskOffice was set to run for an older Windows, or the error started right after a Windows upgrade.

Compatibility mode makes Windows pretend to be an older version for that program. Current Office is built for Windows 11 and 10, and running it as if on Windows 8 or 7 can make it load its libraries wrongly.

1. Open Start, type the app name, for example Word, right-click it and select Open file location.
2. Right-click the app's shortcut and select Properties.
3. Open the Compatibility tab.
4. Clear Run this program in compatibility mode for and any other ticked box there.
5. Select Apply and OK, then open the app.

The tab and its options are explained in How to run a program as administrator or in compatibility mode. Here you only clear them; do not turn compatibility mode on for Office.

Fix 5. Test Office in a new Windows user account

15 minutesLow riskOffice crashes for you, but you suspect it would work for someone else on the same PC.

Office keeps add-ins, templates and settings per user. An answer on the Microsoft Q&A mso.dll thread suggests a new Windows user account to rule out a damaged profile. If Office works there, the problem is in your profile, not in mso.dll.

1. Create a new local account: Create a new user account to test a problem.
2. Sign out and sign in to the new account.
3. Open the Office app that crashed and do the same action.
4. If it works, return to your account and move your files and settings over, or keep removing add-ins and templates in your own profile.

Fix 6. Uninstall Office completely and install one version again

30 to 40 minutesRead the warningRepair fails, two Office versions are on the PC, or an earlier removal stopped halfway.

When two Office versions share the same Microsoft Shared folder, or an old removal left half of one behind, each can load the other's mso.dll. A clean removal and one fresh installation leaves a single matching set of files.

1. Open Settings > Apps > Installed apps and search for office and 365.
2. If two Office versions are listed, decide which one you keep.
3. Uninstall every Office entry: Uninstall a program or app in Windows.
4. Restart the PC.
5. Sign in at your Microsoft account page and install Office again, or run the setup of your licensed version.

Fix 7. Check Windows: system files and a malware scan

30 to 45 minutesNo riskOther programs crash too, or the Office installation and repair both fail.

SFC and DISM repair Windows files that Office relies on, not mso.dll itself, and a malware scan rules out a file that was changed or blocked. Both are general checks, so they come last.

1. Repair Windows system files: Run DISM and SFC to repair Windows system files.
2. Restart the PC.
3. Run a full scan with Microsoft Defender: How to scan for malware with Microsoft Defender.
4. Repair Office again with Fix 2 after the scans.

If the mso.dll error comes back: read the crash in Event Viewer

Each Office crash writes an entry with the faulting application, the faulting module and its path. That is where searches like faulting module path: c:\program files\common files\microsoft shared\office16\mso.dll come from.

1. Press Win + R, type eventvwr.msc and press Enter.
2. Open Windows Logs > Application.
3. Select Filter Current Log, type 1000 in the event ID box and select OK.
4. Open the entry from the time of the crash, with source Application Error.
5. Note Faulting application name, Faulting module name with its version, and Exception code.

• Exception code 0xc0000005 is an access violation: code inside mso.dll read memory it should not. It points to bad data, often from an add-in, not to a missing file.
• A module version older than the app's version means the Office files are out of step. Run Online Repair (Fix 2).
• What to send to Microsoft support: the event text, your Office version from File > Account, and what you did when it crashed.
• When it is hardware: many unrelated programs crash at random times, also with other modules. Test the memory: How to test your RAM with Windows Memory Diagnostic.

How to keep mso.dll errors from coming back

Office 2016 and Office 2019 left support on 14 October 2025, and Windows 10 did the same day. They still run, but they get no fixes for new crash bugs. A supported Office on Windows 11 gets those fixes through Update Options.

Frequently asked questions

What is mso.dll?

mso.dll is the Microsoft Office shared library. Word, Excel, Outlook, PowerPoint, Access and Publisher all load it for shared parts such as the ribbon, file dialogs, spelling and add-in support. It is installed by Office in the Microsoft Shared folder under Common Files, not by Windows. A crash report that names it tells you Office crashed, but not why. The cause is usually an add-in or a damaged Office installation.

Where is mso.dll located?

For Microsoft 365 and Office 2016 to 2024 on 64-bit Windows, it is in C:\Program Files\Common Files\Microsoft Shared\OFFICE16. A 32-bit Office uses the same path under Program Files (x86). Office 2010 keeps it in the office14 folder. If the file is missing from your Office folder, repair Office instead of copying it from somewhere else, because it must match the exact build of the rest of Office.

Can I download mso.dll and put it in the folder?

Do not do that. An Office build expects the mso.dll of exactly the same version, so a file from a DLL site rarely matches and can make crashes worse. Such files can also carry malware. Repairing Office downloads or restores the correct file for your installation in a few minutes. If repair fails, uninstall Office and install it again from your Microsoft account.

Why does Outlook crash with an mso.dll error?

Most often an Outlook add-in, such as a mail scanner, a CRM connector or an old meeting plug-in, crashes inside mso.dll when you send or open mail. Start Outlook with outlook /safe from Win + R. If it works there, turn off COM add-ins one at a time in File, Options, Add-ins. If Outlook also crashes in Safe Mode, run Online Repair of Office.

Why does mso.dll use high CPU?

mso.dll does not run on its own, so Task Manager shows the Office app, not the DLL. Because so many shared features live in mso.dll, a busy Office app often spends its time there. High CPU in an Office app usually comes from an add-in, a large file with live calculations, or a background Office task. Test the app in Safe Mode first. For the Office SDX Helper process, see our guide to Microsoft Office SDX Helper high CPU.

What does msointl.dll missing mean?

msointl.dll is the language resource file of Office. It holds the interface text for a language, so it sits next to the language pack rather than in the shared folder. When it is missing, usually after a language pack was removed or an update stopped halfway, the app shows an error at start. The fix is the same as for mso.dll: run Online Repair of Office, and if you removed a language, add it back from Office language settings.

What is mso9.dll?

mso9.dll is the shared library of Office 2000, the ninth version of Office. It is named in errors only on PCs that still run Office 2000 or an old program that installed parts of it. That Office is far past its end of support and cannot be repaired online. The practical fix is to install a current Office. Do not download mso9.dll from a DLL site.

Does SFC repair mso.dll?

No. System File Checker repairs protected Windows files, and mso.dll belongs to Office, not to Windows. SFC and DISM help only when Windows itself is damaged, for example when other programs crash too. For mso.dll, use Office repair: Installed apps, then Microsoft 365 or Office, then Modify, then Quick Repair or Online Repair. That is the tool that checks and replaces Office files.

Does re-registering mso.dll with regsvr32 fix the error?

We found no Microsoft source that recommends it, and it is not needed. Office setup and repair register what Office needs. If regsvr32 reports that the module could not be loaded or that the entry point was not found, that does not mean Office is broken. Use Office Safe Mode for crashes and Office repair for a missing file instead.

Is the mso.dll error a sign of a virus?

Rarely. In almost all reported cases the cause is an add-in or a damaged Office installation. Malware can damage or replace DLL files, so if Office repair keeps failing, or other programs also behave oddly, run a full scan with Microsoft Defender. A real risk comes from DLL download sites: a downloaded mso.dll is a much more likely way to get malware than the error itself.