fsmuiav.dll Won’t Load: Rebuild the F-Secure App Safely

The exact fsmuiav.dll errors

You may see one of these messages when Windows starts an old F-Secure component:

• “This application failed to start because fsmuiav.dll was not found.”
• “The file fsmuiav.dll is missing or corrupted.”
• “A required component is missing: fsmuiav.dll. Please install the application again.”
• “Error loading fsmuiav.dll. The specified module could not be found.”
• “The program can’t start because fsmuiav.dll is missing from your computer.”
• “Cannot register fsmuiav.dll.”

fsmuiav.dll is an F-Secure application file, not a Windows system DLL. The safe repair is to repair or reinstall the F-Secure installation that owns it, rather than downloading a replacement file into System32.

The 60-second answer

fsmuiav.dll is associated with the F-Secure Anti-Virus user interface. Its reported description is “FSAV FSM AV UI”, and historical F-Secure installations placed it in application folders such as:

C:Program FilesF-SecureFSGUI

Older ISP-branded F-Secure products could use similar directories. The file is a legacy, narrow component, and there is no reason to expect it in C:WindowsSystem32 or C:WindowsSysWOW64.

Use this order:

1. Check whether F-Secure is still installed.
2. Repair or reinstall F-Secure from its official installer.
3. If removal is broken, use F-Secure’s official Windows Uninstallation Tool.
4. Check Windows Security Protection History before restoring a quarantined file.
5. Run Windows repair commands only if Windows itself has broader corruption symptoms.
6. Remove F-Secure completely if you no longer need the obsolete installation.

Do not use a DLL download site, copy the file from another computer, or run regsvr32 as a first response.

What causes fsmuiav.dll to disappear

The most likely causes are related to the F-Secure installation itself.

Damaged or incomplete F-Secure installation

An interrupted update, failed uninstall, disk cleanup, or partially removed product can leave a shortcut or startup entry pointing to fsmuiav.dll after the file has gone.

This is the most likely explanation when the error names an F-Secure executable or appears immediately after removing or upgrading F-Secure.

Antivirus quarantine

Windows Security or another security product may have quarantined the file. A detection does not automatically prove that the file was malicious, but it also does not make restoration safe by itself.

Check the file’s original location, publisher signature, and whether the F-Secure installation is trusted before restoring anything.

Old startup entry remains

If F-Secure was uninstalled incompletely, Windows may still try to launch an old tray program, service, scheduled task, or shortcut. Reinstalling a DLL alone will not repair that stale reference.

Mixed or incompatible files

Copying one DLL from another installation can create a version or dependency mismatch. A file may exist but still fail to load because another F-Secure module is missing, has the wrong architecture, or belongs to a different product build.

Broader Windows corruption

Windows corruption is possible but less likely. fsmuiav.dll belongs to an application, so System File Checker does not normally recreate it. Use Windows repair commands only when other Windows components are also failing or the F-Secure installer cannot run.

Malware or tampering

A file with the correct name is not automatically legitimate. A copy found in a temporary folder, a user profile, System32, or an unrelated application directory should be treated cautiously until its publisher and location are verified.

Fix 1: identify what is requesting the file

Before changing anything, capture the exact program named in the error.

1. Write down the executable name shown in the dialog.
2. Note when the message appears:
3. At Windows sign-in
4. When opening F-Secure
5. When launching another application
6. During shutdown
7. After an update or uninstall
8. Open Settings with Windows + I.
9. Select Apps, then Installed apps.
10. Search for F-Secure.
11. If it is listed, note the product name and whether an Uninstall option is available.

If the dialog names an F-Secure executable, continue with the F-Secure repair steps. If it names an unrelated program, do not assume that program owns the DLL. The stale request may be coming from an old F-Secure startup component.

If F-Secure is not installed, look for a leftover entry:

1. Press Ctrl + Shift + Esc to open Task Manager.
2. Select Startup apps.
3. Look for F-Secure entries or an item marked Disabled whose location refers to F-Secure.
4. Right-click an entry and select Open file location, if available.
5. Do not delete files yet. First confirm that F-Secure is no longer needed.

You can also check Settings → Apps → Startup. Disable only a confirmed leftover F-Secure startup item. This may stop the message, but a complete uninstall is preferable.

Fix 2: repair or reinstall F-Secure

If F-Secure is still installed, use its own repair or setup process. The exact button names vary by product and age, but the principle is the same: restore the complete application, not one DLL.

Try the installed product first

1. Close all F-Secure windows.
2. Restart Windows.
3. Open Settings → Apps → Installed apps.
4. Select the F-Secure product.
5. If Windows offers Advanced options, open it.
6. Use Repair only if that option is present.
7. Follow the installer prompts.
8. Restart Windows again.

If no repair option appears, download the current F-Secure product installer from F-Secure’s official support or product page. Do not search for fsmuiav.dll itself.

Run the installer normally first. If Windows blocks a required action:

1. Right-click the official F-Secure installer.
2. Select Properties.
3. If an Unblock checkbox appears on the General tab, select it and choose Apply.
4. Right-click the installer again.
5. Select Run as administrator.
6. Choose the option to repair, upgrade, or install the complete F-Secure product.

How to tell whether it worked

The repair is successful when:

• The F-Secure application opens without the DLL error.
• The warning no longer appears after restarting Windows.
• F-Secure’s protection status loads normally.
• The installation directory contains the required files.
• No new missing-DLL message appears for another F-Secure component.

Do not judge success solely by whether a file with the right name exists. The application must start and its protection features must operate normally.

Fix 3: use the official F-Secure uninstaller when removal is broken

Use this step when ordinary uninstall fails, the installer says that an older version is already present, or Windows repeatedly reports a missing F-Secure component after removal.

F-Secure provides an official Uninstallation Tool for Windows through its support tools page. The vendor describes it as a last resort when normal uninstallation cannot remove the product.

1. Save your work and close other applications.
2. Download the uninstallation tool from F-Secure’s official support tools page.
3. Right-click the downloaded tool and select Run as administrator.
4. Follow the prompts to remove F-Secure.
5. Restart Windows when requested.
6. Check Settings → Apps → Installed apps and confirm that the old F-Secure product is gone.
7. Check Task Manager → Startup apps for remaining F-Secure entries.
8. Install the current supported F-Secure product only if you still need it.

The uninstaller may remove protection components and settings. Read its prompts carefully before proceeding.

If you no longer use F-Secure, complete removal is the correct fix. Do not reinstall an obsolete product merely to supply one legacy DLL.

Fix 4: inspect quarantine before restoring anything

If the error began after a security scan, check whether the file was quarantined.

1. Open Windows Security from the Start menu.
2. Select Virus & threat protection.
3. Select Protection history.
4. Open the detection related to fsmuiav.dll.
5. Review the original file path, detection name, and action taken.
6. Confirm whether the path belongs to an F-Secure installation directory.

Microsoft explains the available actions in its Protection History documentation.

Restore the file only when all of these conditions are true:

• F-Secure is a trusted installation.
• The original path is an F-Secure application directory.
• The file can be verified as published by F-Secure Corporation.
• The detection appears to be a false positive rather than an active threat.
• You are prepared to reinstall F-Secure if verification fails.

If the file was found outside an F-Secure directory, do not restore it merely because the filename matches. Reinstall the complete application from F-Secure instead.

If the detection is unclear, leave the file quarantined and run a full scan. Microsoft’s Virus & threat protection guidance explains how to start additional scans.

Fix 5: verify the file’s location and signature

If fsmuiav.dll still exists, verify it before attempting any manual change.

1. Open File Explorer.
2. Browse to the F-Secure installation directory.
3. Right-click fsmuiav.dll.
4. Select Properties.
5. Open the Digital Signatures tab, if present.
6. Select the signature and choose Details.
7. Confirm that Windows reports a valid signature and that the signer is F-Secure Corporation.

A valid signature is useful evidence, but it does not replace reinstalling the product when the installation is incomplete.

The location matters:

• An F-Secure FSGUI or related application folder is consistent with historical installations.
• C:WindowsSystem32 is not an expected destination for this application-owned file.
• C:WindowsSysWOW64 is also not a general-purpose destination for it.
• A game folder, browser folder, download folder, or temporary directory requires investigation.

Do not move the file into another directory to satisfy an error. The requesting executable and its dependent files must be repaired together.

Fix 6: do not use regsvr32 for this DLL by default

A common suggestion is:

regsvr32 fsmuiav.dll

That is not a general DLL repair command. Microsoft documents regsvr32 as a tool for registering self-registering COM and OLE components, including ActiveX controls. A user-interface library that does not expose DllRegisterServer will fail with a registration error, and registration cannot restore missing dependent files.

Do not register fsmuiav.dll unless F-Secure’s own instructions specifically require it. For this file, repairing or reinstalling the complete F-Secure product is the appropriate path.

Fix 7: repair Windows components only when Windows is also damaged

SFC and DISM repair protected Windows components. They are not designed to download or recreate an F-Secure application DLL.

Use them when you also see symptoms such as damaged Windows features, unexplained system file errors, failed Windows components, or an F-Secure installer that cannot run because Windows itself appears corrupted.

First install pending Windows updates:

1. Open Settings.
2. Select Windows Update.
3. Select Check for updates.
4. Install available updates.
5. Restart Windows.

Microsoft’s Windows Update instructions cover this process.

Then open an elevated Command Prompt:

1. Open the Start menu.
2. Type Command Prompt.
3. Right-click Command Prompt.
4. Select Run as administrator.
5. Approve the User Account Control prompt.
6. Run:

DISM.exe /Online /Cleanup-image /Restorehealth

Wait for it to finish. Then run:

sfc /scannow

Microsoft recommends running DISM before SFC. The official System File Checker guidance explains the result messages.

Restart after both commands complete, then repair or reinstall F-Secure again.

Outbyte PC Repair can scan for broader Windows problems when you are tired of repeating SFC and DISM without knowing what changed; its free scan shows detected issues, while repair requires the full version. It is optional, and reinstalling F-Secure remains the definitive fix for this application-owned DLL.

What the results mean

• Windows Resource Protection did not find any integrity violations: Windows protected files appear intact. Focus on F-Secure.
• Windows Resource Protection found and repaired corrupt files: Restart, then retry the F-Secure repair.
• Windows Resource Protection found files but could not repair some: Review the SFC output and address Windows corruption separately.
• DISM fails: Record the error, restart, install pending updates, and retry once. Do not use the failure as a reason to download fsmuiav.dll.

Fix 8: use System Restore only after a recent system change

System Restore may help if the error began immediately after an installation, update, driver change, or cleanup operation. It rolls back system files, registry settings, drivers, and installed programs while preserving personal files.

1. Press Windows + R.
2. Type:

rstrui.exe

1. Press Enter.
2. Select Next.
3. Choose a restore point created before the error began.
4. Select Scan for affected programs if available.
5. Review the changes.
6. Select Finish and allow Windows to restart.

Microsoft’s System Restore documentation explains what is changed.

System Restore is not a substitute for reinstalling F-Secure. If the restore does not help, use the official F-Secure repair or uninstallation path.

Fix 9: update drivers only when the evidence points to a driver problem

fsmuiav.dll is not identified as a hardware driver. Device Manager is therefore not a first-line repair tool for this error.

Use Device Manager only if the same incident includes hardware failures, yellow warning icons, display problems, network failures, or a driver installation that immediately preceded the message.

1. Right-click the Start button.
2. Select Device Manager.
3. Expand the category related to the failing hardware.
4. Right-click the device.
5. Select Update driver.
6. Choose Search automatically for drivers.
7. Restart Windows if a driver is installed.

Do not remove random devices in Device Manager to fix an application DLL.

Outbyte Driver Updater can reduce the work of hunting through many hardware vendors and guessing which driver is stale; its free scan identifies available updates, while installation requires the full version. It is optional, and it will not replace the complete F-Secure reinstall this error usually requires.

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32-bit and 64-bit considerations

Do not select a replacement DLL based only on whether Windows is 32-bit or 64-bit.

A 64-bit edition of Windows can run both 64-bit and 32-bit applications, while a 32-bit application needs compatible application components. The correct architecture depends on the F-Secure executable and the product build that installed it.

That is why copying a file from another computer is unreliable:

• The copied file may belong to another F-Secure release.
• Its architecture may not match the requesting executable.
• Its dependent files may be missing.
• Its signature may not be valid.
• It may have been altered or bundled with malware.

The complete F-Secure installer selects and installs the matching set of files.

Why random DLL downloads are unsafe

Do not download fsmuiav.dll from a DLL catalogue, file mirror, forum attachment, or software bundle.

A standalone download can be:

• Malicious or modified.
• The wrong version.
• The wrong architecture.
• Missing required dependencies.
• Unsigned or signed by an unexpected publisher.
• Unable to fix the stale startup entry that caused the message.

Putting it in System32, SysWOW64, an application folder, or a game directory can create conflicts and make later removal harder. The safe source is the official F-Secure installer or its official Windows uninstallation tool.

If the error remains after reinstalling

Collect these details before attempting another repair:

1. The exact error text.
2. The executable named in the dialog.
3. The full path where Windows expects fsmuiav.dll.
4. Whether F-Secure is currently installed.
5. The F-Secure product name and version shown in Installed apps.
6. Whether the file exists in the F-Secure installation directory.
7. Whether its digital signature is valid.
8. Whether Windows Security quarantined it.
9. Whether the error started after an update, uninstall, cleanup, restore, or malware scan.
10. Whether the problem occurs in Safe Mode or only during normal startup.

If the file is present but still will not load, another F-Secure dependency may be missing. Reinstall the complete matching product rather than replacing individual files.

If F-Secure is no longer wanted, run the official uninstallation tool, restart, and remove the remaining confirmed startup reference. Do not keep repairing a legacy installation that you no longer use.

FAQ

Is fsmuiav.dll part of Windows?

No. Available evidence identifies it as an F-Secure application DLL with the description “FSAV FSM AV UI.” It should not be treated as a Microsoft system component.

Does F-Secure still use this file?

The file appears to be associated mainly with historical F-Secure Anti-Virus and GUI components. Do not assume that every current F-Secure product still ships it. Use the current official installer rather than trying to preserve an old file.

Should I put it in System32?

No. It is application-owned, and there is no reliable reason to place it in a Windows system directory.

Should I reinstall Visual C++, DirectX, or .NET?

Not as a first step. There is no established evidence that fsmuiav.dll is a Visual C++, DirectX, or .NET component. Repair F-Secure first.

Can I register it with regsvr32?

Usually not. regsvr32 applies to self-registering COM/OLE DLLs and ActiveX controls. Registration does not restore a damaged F-Secure installation or its dependencies.

What if Microsoft Defender quarantined it?

Review Windows Security → Virus & threat protection → Protection history. Restore only after confirming the original F-Secure location and publisher signature. Otherwise leave it quarantined and reinstall F-Secure from its official source.

What if the message appears when starting a game?

The game may not own the file. Record the executable named by Windows and check for an old F-Secure startup component. Do not copy the DLL into the game folder.

What is the final fix if I no longer use F-Secure?

Remove F-Secure completely. If normal uninstall fails, use F-Secure’s official Windows Uninstallation Tool, restart, and verify that the stale startup entry is gone.

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