FIX: LogonUI.exe Error on BOOT/Start-up

LogonUI.exe crashes at the Windows login screen, often showing errors like “memory could not be read” or “stack-based buffer overrun.” This can cause the computer to keep restarting or show a black screen, and you may not be able to get into Safe Mode.

This error means the login screen process stopped working because of problems with memory or instructions during startup. The most common cause is a damaged display (graphics) driver. Other possible causes are hard drive problems, damaged system files, viruses, or failed Windows updates.

Our guide below will help you address both possible causes, along with other potential reasons for this error.

1. Run DISM Repair

Sometimes, this error appears because the LogonUI program is damaged. We’re going to walk you through using a Windows repair tool called DISM. To use it, you’ll need to boot into Safe Mode with Command Prompt.

1. Power on your computer, then forcefully shut down your PC as soon as you see the Windows logo.
2. Repeat this step 4 or 5 times. Eventually, you’ll see a screen that says Preparing Automatic Repair. When you see this, let it run.
3. On the Automatic Repair screen, click on Advanced Options > Troubleshoot > Advanced Options > Command Prompt.
4. When the black Command Prompt window opens, type:

   Dism /Online /Cleanup-Image /RestoreHealth

   and press Enter.

Windows will check and repair any system files that are corrupted.

Once this process finishes, see if the issue is resolved. If you still have the error, you might need to repair your system files using Windows installation media.

To do this, create an installation media by following Method 5 in our guide here. Once you get to Advanced Options, select Safe Mode with Command Prompt.

Now your PC will boot into safe mode with a command prompt window.

First, find the drive letter of your installation media by typing:
D: and pressing Enter. If you see folders like boot, efi, sources, you’ve found it. If not, try E:, F:, etc. and note the correct drive letter. For this example, let’s assume it’s D:.

Next, type:

Dism /Image:C:\ /Cleanup-Image /RestoreHealth /Source:wim:D:\Sources\Install.wim:1 /limitaccess 

(Replace D: with the letter for your installation media, if needed.)

Once the process is complete, restart your computer. The problem should be fixed. If not, move on to the next solution.

2. Uninstall FastAccess or Other Security Programs

Some facial recognition programs, like FastAccess, or other security software, can sometimes conflict with Windows and cause this error.

1. Power on your computer, then forcefully shut down when you see the Windows logo.
2. Repeat this step 4–5 times until you see Preparing Automatic Repair under the Windows logo, then let it run.
3. On the Automatic Repair screen, select Advanced Options > Troubleshoot > Advanced Options > Startup Settings.
4. Click Restart.
5. When you reach the Startup Settings screen, press F4 to enter Safe Mode.
6. Once in Safe Mode, hold down the Windows key and press R. Type appwiz.cpl and press Enter.
7. Look for FastAccess or any similar security program. Right-click it and select Uninstall.

If the LogonUI error appears even in Safe Mode (making you unable to log in), follow the instructions from Solution 1 to access Command Prompt. Then:

1. Type:

   ren "C:\Program Files" "Program Files-old"

   and press Enter.

2. Next, type:

   ren "C:\Program Files (x86)" "Program Files (x86)-old"

   and press Enter.
   If you get an error, don’t worry—just continue.

3. Restart your computer and try to log in normally.
4. Once you’re in, go to your C: drive and rename the folders back to Program Files and Program Files (x86) by removing the -old.
5. Again, press Windows key + R, type appwiz.cpl, and uninstall any security software that looks suspicious.
6. Restart your system and check if the issue is resolved.

3. Disable Graphics Card Adapter

A temporary issue with your graphics adapter can also cause LogonUI to fail. To fix this, disable the graphics adapter in Safe Mode, then update and enable it in normal mode.

1. Boot into Safe Mode following our guide here.
2. Once you’re in Safe Mode, press Windows key + R. Type devmgmt.msc and press Enter to open Device Manager.
3. Expand Display Adapters, right-click your graphics device, and choose Disable.
4. Restart your computer. You should now be able to log in normally.
5. To re-enable, open Device Manager again, right-click your graphics device, and select Enable.
6. Next, right-click and choose Update Driver Software.
7. Click Search automatically for updated driver software.