How to Fix Authui.dll Not Found or Missing Errors

Authui.dll errors are caused by situations that lead to the removal or corruption of the Windows Authentication UI DLL file.

In some cases, authui.dll errors could indicate a registry problem, a malware issue like a virus infection, or even a hardware failure.

Authui.dll Errors

There are several ways authui.dll error messages might be phrased, depending on the cause of the problem:

• Authui.dll Not Found
• The file authui.dll is missing.
• This application failed to start because authui.dll was not found. Re-installing the application may fix this problem.
• Cannot find [PATH]\authui.dll
• Cannot start [APPLICATION]. A required component is missing: authui.dll. Please install [APPLICATION] again.
• C:\Windows\system32\authui.dll is either not designed to run on Windows or it contains an error.

These error messages might appear while using or installing certain programs, when Windows starts or shuts down, or maybe even during a Windows installation. Noting at what point the error shows up for you is an important piece of information that will be helpful during troubleshooting.

How to Fix Authui.dll Errors

Follow these steps in the order they're given below to try the simpler solutions first.

1. Restore authui.dll from the Recycle Bin. The easiest possible cause of a "missing" authui.dll file is that you've mistakenly deleted it.

   If you suspect this, but you've already emptied the Recycle Bin, you may be able to recover the file with a free data recovery program.

   Start Windows in Safe Mode to complete this step, or any of the following steps, if you're unable to access Windows normally due to the error.

2. Scan your entire computer for viruses and other malware. Some authui.dll errors could be related to some kind of malware infection on your computer that has damaged the DLL file.

   It's even possible that the authui.dll error you're seeing is related to a hostile program that's masquerading as the file.

3. Execute the sfc /scannow command to replace a missing or corrupt copy of the authui.dll file. Fortunately, the authui.dll file is provided by Microsoft in at least some versions of Windows, so the System File Checker tool (the sfc command) should restore it.

   This is the most likely solution to a missing or not found authui.dll error. Please make every effort you can to complete this step after making sure your computer isn't infected with malware.

4. Use System Restore to undo recent system changes. If you suspect that the authui.dll error was caused by a change made to an important file or configuration, and System File Checker didn't help, System Restore should solve the problem.

5. Reinstall the program that uses the authui.dll file. If the DLL error occurs when you use a particular program, reinstalling the program should replace the file.

   This step is most useful for replacing DLL files that are not supplied by Microsoft, but it could help with your authui.dll problem if this program also provides a copy of the file and the previous troubleshooting ideas weren't successful.

6. Update the drivers for hardware devices that might be related to authui.dll. If, for example, you're receiving a "The file authui.dll is missing" error when you play a 3D video game, try updating the drivers for your video card.
   

   The authui.dll file may or may not be related to video cards—this was just an example. The key here is to pay very close attention to the context of the error and troubleshoot accordingly.

7. Roll back a driver to a previously installed version if authui.dll errors began after updating a particular hardware device's driver.

8. Install any available Windows updates. Many service packs and other patches replace or update some of the hundreds of Microsoft distributed DLL files on your computer. The authui.dll file could be included in one of those updates.

9. Repair your installation of Windows. If the individual authui.dll file troubleshooting advice above is unsuccessful, performing a Refresh, Startup Repair, or Repair Installation (depending on your version of Windows) should restore all Windows DLL files to their working versions.

10. Use a free registry cleaner to repair authui.dll related issues in the registry. A free registry cleaner program may be able to help by removing invalid authui.dll registry entries that might be causing the DLL error.
    

    We rarely recommend the use of registry cleaners. They're included here just in case it turns out to be helpful, in which case you could avoid the more difficult testing and last-resort options below.

11. Test your memory and then test your hard drive. We've left the majority of hardware troubleshooting to the last step, but your computer's memory and hard drive are relatively easy to test and are the most likely components to cause authui.dll errors as they fail.

    If the hardware fails any of your tests, replace the memory or replace the hard drive as soon as possible.

12. Perform a clean install of Windows. This will erase everything and install a fresh copy of Windows. If none of the steps above correct the authui.dll error, this should be your next course of action.

    To be clear, all the data on the drive you have Windows installed on will be deleted during this step, so be sure to back up important files if you're able to. Obviously, make sure you've made every attempt possible to fix the authui.dll error using a troubleshooting step prior to this one before you take on a clean installation.

13. Troubleshoot for an unknown hardware problem if any authui.dll errors persist.

    A clean Windows installation is a fresh start on the software-side of the troubleshooting. So, unfortunately, if that didn't work, your DLL problem must be hardware related.

Need More Help?

If you're not interested in fixing this problem yourself, see How Do I Get My Computer Fixed? for a full list of your support options, plus help with everything along the way like figuring out repair costs, getting your files off, choosing a repair service, and a lot more.