Start with this diagnostic checklist
Before changing files, note:
- Which program shows the error? If the message appears before sign-in, after
Ctrl+Alt+Delete, or during a UAC credential prompt, it may be a Windows logon problem rather than an application problem. - When did it begin? Check whether it followed Windows Update, antivirus activity, malware removal, a cleanup utility, a driver installation, or logon customization.
- Can you reach the desktop? If not, use Windows Recovery Environment steps later in this guide.
- Which Windows architecture is installed? Open Settings → System → About and check System type. On 64-bit Windows,
System32contains native 64-bit system files. It is not a 32-bit folder. - Is another DLL named in the same dialog? Repairing
authui.dllwill not fix a separate missing dependency.
authui.dll is a genuine Microsoft Windows component, not a Visual C++ Redistributable, DirectX, .NET, game, or ordinary application runtime. The safest repair is to repair Windows itself, not to download a replacement DLL.
What authui.dll does
authui.dll is associated with the Windows Authentication UI. Windows uses it as part of the credential-provider system that presents authentication interfaces, while LogonUI.exe loads the providers used for interactive sign-in. Microsoft documents the component under %SystemRoot%System32.Microsoft Windows Internals sample
The normal native path is:
%SystemRoot%System32authui.dll
On 64-bit Windows, this normally means:
C:WindowsSystem32authui.dll
Windows also maintains compatibility locations for 32-bit components, including C:WindowsSysWOW64. Do not decide where to copy a file based only on whether Windows is 32-bit or 64-bit. Servicing tools select the correct component for the installed build.
A version or file size seen on another computer is not a universal reference. The correct file depends on the Windows edition, architecture, language, servicing level, and build. Do not replace it with a file from another Windows installation.
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What the error messages mean
You may see wording such as:
- “The program can’t start because authui.dll is missing from your computer.”
- “The code execution cannot proceed because authui.dll was not found.”
- “authui.dll was not found.”
- “LogonUI.exe – Bad Image.”
- “authui.dll is either not designed to run on Windows or it contains an error.”
- “Windows could not start because authui.dll is missing or corrupt.”
A message during an ordinary application launch can indicate that Windows authentication components are damaged, but the application may also be naming another dependency nearby in the failure chain. A message at the sign-in screen, after Ctrl+Alt+Delete, or during a credential prompt points more directly to LogonUI.exe, Windows servicing, security software, or a third-party credential provider.
“Missing” does not always mean the file is absent. The file may be present but corrupted, unsigned, the wrong architecture, from the wrong Windows build, or blocked after antivirus quarantine.
Fix 1: Restart, then install pending Windows updates
A restart can complete a pending component replacement or update transaction.
- Save your work.
- Select Start → Power → Restart.
- After Windows starts, open Settings.
- Select Windows Update.
- Select Check for updates.
- Install all available updates and restart when requested.
Microsoft provides the standard update procedure here.Install Windows updates
Try the action that originally produced the error. If the message returns, continue with component repair.
Fix 2: Repair Windows with DISM and SFC
This is the most important fix for a missing or damaged authui.dll. DISM repairs the Windows component store, and System File Checker verifies protected files and replaces damaged copies.
- Open Start and type
Command Prompt. - Right-click Command Prompt and select Run as administrator.
- Select Yes at the User Account Control prompt.
- Run this command:
DISM.exe /Online /Cleanup-Image /RestoreHealth
- Wait for it to complete. Do not close the window if progress appears to pause.
- Run SFC afterward:
sfc /scannow
- When both commands finish, restart Windows.
Microsoft documents DISM image repair and the SFC command.
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A successful result is an SFC message saying that Windows Resource Protection found no integrity violations, or that it found corrupt files and successfully repaired them. Test sign-in or the affected credential prompt.
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- Run DISM again.
- Restart.
- Run
sfc /scannowagain. - If the problem remains, review
%windir%LogsCBSCBS.logor continue to the repair-installation options below. DISM may use Windows Update or a matching repair source when the local component store is incomplete.
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Fix 3: Check antivirus quarantine before restoring anything
Security software may quarantine a genuine system file, but malware can also use a familiar filename. Do not restore authui.dll merely because the name looks legitimate.
For Microsoft Defender:
- Open Windows Security from the Start menu.
- Select Virus & threat protection.
- Select Protection history.
- Review the detection details and path.
- If the detection is confirmed false and the file is identified as a genuine Microsoft-signed Windows component, use the available Restore action.
- Restart Windows.
- If authenticity is uncertain, leave it quarantined and run DISM followed by SFC instead.
- Return to Virus & threat protection, select Scan options, choose Full scan, and select Scan now.
Microsoft explains the available quarantine and restore actions in Protection history.
If malware is suspected, do not whitelist the file just to make the error disappear. Repair Windows after the scan, and use official recovery media if the system remains compromised.
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Fix 4: Remove a conflicting credential provider or logon customizer
Fingerprint readers, smart-card packages, corporate authentication agents, and logon customizers can interact with LogonUI.exe. A recent installation or update can therefore trigger an authentication failure without owning authui.dll.
If you can sign in:
- Open Settings → Apps → Installed apps.
- Sort by Date installed if available.
- Identify recently installed fingerprint, smart-card, security, remote-access, or logon-customization software.
- Select its three-dot menu and choose Uninstall, or use the vendor’s official uninstaller.
- Restart.
- Install a current package from the hardware or software vendor only after Windows sign-in works.
For a recently installed Windows update, open Settings → Windows Update → Update history → Uninstall updates. Remove only the update that clearly matches the beginning of the problem, then restart. System Restore is another suitable rollback when the failure began after a system change.
Update related device software
If the problem began after a fingerprint reader, smart-card device, camera, or security-device change:
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- Right-click Start and select Device Manager.
- Expand the relevant category, such as Biometric devices, Smart card readers, Cameras, or Security devices.
- Right-click the affected device and select Properties.
- Check the General tab for an error status.
- Open the Driver tab.
- Use Roll Back Driver if the button is available and the issue began immediately after an update.
- Otherwise select Uninstall Device, restart, and install the correct driver from the device manufacturer’s official support page.
Manually hunting through driver versions can be tedious, especially when several authentication devices are installed. Outbyte Driver Updater can use its free scan to identify outdated drivers, while driver installation is handled by the full version; it is optional and is not a replacement for repairing Windows or reinstalling the responsible credential-provider package.
Do not treat a driver update as a repair for authui.dll itself. It addresses a possible conflict around LogonUI.exe.
Fix 5: Use Windows 11’s repair reinstall
Windows 11 may offer a repair reinstall that keeps your applications, personal files, and settings.
- Open Settings → System → Recovery.
- Find Fix problems using Windows Update.
- Select Reinstall now.
- Follow the prompts.
- Keep the computer connected to power and restart when requested.
This reinstalls the same Windows version and can restore damaged system components without a conventional clean installation. If the option is not present or does not solve the issue, use matching official installation media.
Fix 6: Perform an in-place repair from official installation media
An in-place repair replaces Windows components while preserving the selected data.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems- Obtain official Windows installation media that matches the installed Windows release and architecture.
- Mount the ISO or insert the official installation media.
- Open the media in File Explorer.
- Run
setup.exe. - Follow the installer prompts.
- Select Change what to keep.
- Choose Keep personal files and apps.
- Confirm the selection and start the installation.
- Let Windows restart as needed.
Do not start by booting from the media if your goal is to preserve applications. Starting setup.exe inside Windows is the path used for an in-place repair. Microsoft’s procedure is described in Reinstall Windows with installation media.
If Windows cannot complete the repair, back up important data and consider a clean installation, particularly after confirmed malware or severe system corruption.
If you cannot reach the desktop
Use Windows Recovery Environment:
- Start the computer.
- At the sign-in or recovery screen, select Power.
- Hold Shift and select Restart, if the option is available.
- Select Troubleshoot → Advanced options → Command Prompt.
- Sign in with an administrator account if prompted.
In recovery mode, Windows may not be mounted as C:. Find the Windows drive before running offline repairs:
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diskpart
list volume
exit
Check likely drive letters:
dir C:Windows
dir D:Windows
When you identify the correct letter, use offline SFC, replacing D: below if necessary:
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If the repair environment can access a matching Windows source, DISM may also be used with an appropriate /Source path. Avoid guessing source paths or copying a DLL from another computer.
For rollback, open Troubleshoot → Advanced options → System Restore, or open Command Prompt and run:
rstrui.exe
Choose a restore point from before the error began. System Restore normally rolls back system files, settings, drivers, and installed programs without removing personal files. Microsoft describes this recovery method in System Restore.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What not to do
Do not download a loose authui.dll
Random DLL download pages can provide malware, the wrong architecture, the wrong Windows build, or a file with incompatible dependencies. A copied file may also hide the real cause, such as component-store corruption or an antivirus action.
Microsoft does not provide a universal standalone current authui.dll download page. Use Windows Update, DISM, SFC, Windows recovery, or official installation media instead.
Do not copy it from another PC
Even two computers running Windows 10 or Windows 11 may have different editions, builds, languages, architectures, and servicing states. Manual copying can cause “Bad Image,” missing-entry-point, signing, or dependency errors. Whole-component servicing is safer.
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Do not run regsvr32 as a general fix
regsvr32 authui.dll does not restore a missing Windows component. regsvr32 is for DLLs that expose registration functions such as DllRegisterServer; an authentication component may not provide that interface. It can simply produce an entry-point error.Microsoft regsvr32 documentation
Do not reinstall unrelated runtimes
Visual C++ Redistributable, DirectX, and .NET do not own this Windows authentication component. Reinstalling them is unlikely to repair authui.dll.
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Windows Features also is not a repair source for this file. You can inspect Settings → System → Optional features → More Windows features, or run optionalfeatures.exe, but enabling random features will not replace a damaged authentication component.
Verification checklist
After repairing Windows:
- Confirm that the original error no longer appears.
- Test normal sign-in, lock/unlock,
Ctrl+Alt+Delete, and a UAC prompt. - Check that the affected fingerprint, smart-card, or corporate credential provider still works.
- Confirm that Windows Update completes without another rollback.
- If the file exists, inspect its path and properties rather than comparing only its size or version with an online list.
- If another DLL is named in the error, troubleshoot that file separately.
- If the issue returns after a credential-provider installation, remove or update that package before attempting another manual file change.
FAQ
Is authui.dll a third-party application file?
No. It is part of Microsoft Windows and is used by the Windows Authentication UI and LogonUI.exe. An application can expose the error while Windows authentication components are damaged, but the file is not supplied by a game or ordinary app.
Should I install both 32-bit and 64-bit copies?
No. Do not install isolated copies. Windows services the correct architecture and build. On 64-bit Windows, native system files normally reside in System32, while compatibility components may use SysWOW64.
Why does the error appear when launching a program?
The dialog may be triggered while Windows displays a credential prompt, elevated permission request, or sign-in-related interface. It may also name authui.dll alongside another failed dependency. Record the full message before repairing anything.
Can antivirus quarantine cause the problem?
Yes. Check Protection history, but restore only after confirming that the detection is false and the file is an authentic Microsoft-signed system component. Otherwise use a full scan and DISM/SFC.
What if DISM and SFC do not fix it?
Use Windows 11’s repair reinstall if available, then perform an in-place repair from matching official media. If malware or severe corruption is suspected, back up personal data and use a clean installation.
Quick Recap
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