Windows 10 Fall Update (1511) APC_INDEX_MISMATCH

TL;DR: This page is getting a lot of views as the Win 10 deadline approaches. If you have a Dell machine, boot in safe mode or remote in via remote desktop and rename the file “C:\Program Files\Realtek\Audio\HDA\RtkNGUI64.exe”. This should allow you to boot without the blue screen.

So we rolled out the Windows 10 Fall Update (1511) to a couple of PCs at the office that were running Windows 10 RTM. Every machine appeared to upgrade fine, but once any user logged into the PC, it would throw up a frowny-face blue screen stating that “Your computer experienced a problem and needs to restart”. The “if you want to know more” reference was listed as “APC_INDEX_MISMATCH”. Searching around for this points to a driver issue, though there wasn’t really an indication of what exactly it might be.

There wasn’t enough time between the login and the blue screen to do any troubleshooting, but there were a few interesting notes:

  • The PCs could stay at the lock screen or the login screen indefinitely. The blue screen only occurred AFTER logging in. This would indicate that the issue is unlikely to be a driver, as drivers would load prior to logging in.
  • The blue screen appeared after login regardless of network connectivity. Wire plugged in or not, right after hitting the desktop the system would crash. The implication here is that the problem is something already on the PC as opposed to something running in the network logon script.
  • All of the machines were Dell Optiplex desktops, but several different models.

Taking these items together, it would seem to point to a startup program. To test that, we could boot into safe mode (which doesn’t run startup items) and disable them. Microsoft has made it quite a bit harder to get into Safe Mode on Windows 8/10 (especially since this blue screen isn’t happening during startup, so it doesn’t trigger the repair mode automatically), but that is where we needed to turn to solve the problem.

If you aren’t familiar with getting into safe mode on Windows 10 (when you can’t get to the desktop to do it through the menu, anyway), power up the machine and wait for the Windows Logo to appear and the “busy” circle to start spinning at the bottom of the screen. Hold down the power button and shut the machine off before it boots up. Repeat this process a couple of times, and instead of the spinning busy circle, the text “Starting Automatic Repair” will appear. Let this run and you will be presented with a couple of tiles on the screen. Click on the Advanced options tile, and click on Startup Options. You will be asked to reboot again. Do so, and a startup options menu will appear. Select Safe Mode (or safe mode with networking, etc).

To solve this particular problem on our Dell machines, after booting into Safe Mode, open Task Manager, click on Details, and click on the Startup tab. We started by disabling all of the startup programs and rebooting into normal mode. This allowed us to log in without the blue screen.

After that, it was just a matter of starting each of the startup items until we hit a blue screen. The culprit for us turned out to be “Realtek HD Audio Manager”. The executable is located at “C:\Program Files\Realtek\Audio\HDA\RtkNGUI64.exe”. Running this .exe file immediately blue screens every PC we have tried it on that has the fall update installed.

I’m sure there will be an update for this eventually, but since you can’t even run updates while this error persists, it can be a real pain to get your PC back in working order. You can avoid the whole problem by disabling this startup executable prior to updating to the Windows 10 Fall Update.

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  1. Thank you VERY MUCH! I even called Dell support but they sugested a clean install… you save me a lot of work not really needed.

  2. You are a wonderful human being for posting this! Thank you x 9000!

  3. Many thanks for posting this. It resolved the problem on a Dell Latitude E5450.

    I found this post through the site that matched my exact issue. It would have been nice if Microsoft had posted the resolution on their site! I was able to update the audio driver and save the time of going through their complex troubleshooting.

  4. Good day. Can someone please assist me. I have the same issue and been through the process but the disable tab is not lit and won’t allow me to disable the startup apps. How can I resolve this. Thank you.

    • You should be able to open File Explorer and go to “C:\Program Files\Realtek\Audio\HDA\” and rename the file RtkNGUI64.exe (Add an X to it or something) so that the startup link can’t find it. That should accomplish the same thing as disabling it in Task Manager.

  5. Thank you very much for posting this! I had exactly the same problem and you saved me from wasting a bunch of time trying to get help from Dell.

  6. Someone give this man as Oscar! Thanks a lot buddy.

  7. Thank you so much!
    I would never have guessed how to fix it!

  8. I had the same issue. I have Dell Latitude E-5550. I had to check manually by disabling all startup items and finally discovered that it was RtkNGUI64.exe causing the issue. If in your case, if it isn’t the culprit, try to do ‘Clean Boot’ ( – This article describes for Win 7 and Win 8 but iin Win 10 clean boot can be done the same way) and figure out which one is causing the issue.

  9. This saved me so much time! Thank you!

  10. I suffered through three days of failed Windows 10 install attempts and 30 minutes on hold with a useless Dell tech before I found this. Thanks, thanks, thanks, for saving me from a lifetime of 8.1-flavored doom.

  11. Worked as expected on Dell Latitude 3550. Thanks!

  12. Thank You!!! That did the trick. Interesting sidenote, Remote Desktop worked fine. So I was able to use it to disable all the start up items.

  13. This was my problem also. Thank you. You saved me and my client a lot of time and money!

  14. Optiplex 9020M problem fixed. Thank you so much!


  15. Dell Optiplex 9030 AIO, Wouldn’t boot after upgrading to winodws 10, couldn’t get it to boot. Went to safe mode, disabled the realtek service and startup item. booted right up. Thanks. You just saved me hours of time. Oh, and by the way, the sound still works. what does that thing do anyways besides crash my computer?

  16. Months later, upgrading a Dell E7450 Latitude laptop and kept getting this error. A quick net search and this popped up. Suffice to say you saved me hours of troubleshooting and headaches. You’re a hero.


  17. [SOLVED] thank you very much, i have boot up using a usb stick with windows 10, got into cmd, and deleted the said folder. windows is booting up normally now.

    thanks again.

  18. Indeed, it did the job on my E7450 – thanks Kurt

  19. You are an angel! I was so frustrated with this damn thing…. Genius!

  20. BINGO!
    THANK YOU!!!!!!
    I had exactly same issue. Great. Its done. great……

  21. What else could I say?Thank you very much! Strangely, I managed to upgrade 5 Dell Optiplex but of course the last and sixth one was reluctant…

  22. Thanks! Sorted my 2 or 3 Optiplex Systems that crashed after login!

  23. Great timing! Have upgraded dozens of computers over the past year, hit this for the first time today. Will use Remote Desktop to disable it, as suggested!

  24. Worked great. Thank you very much

  25. Had this problem on a Dell Optiplex 3020M and uninstalling Realtek fixed the sad face after login – thanks heaps!

  26. Thanks so much. This works perfectly!

  27. Just for information, if you’re having the same problem and renaming the file mentioned in the post doesn’t work, just delete the whole Realtek folder. Worked for me! Thanks!

  28. solved…thanks, one question, having realtek disabled won’t cause any troubles ??

    • The PC doesn’t actually need that software loaded for the sound to function. I never investigated what it actually was, but I imagine it is some sort of control/configuration software for tweaking audio settings.

  29. Thank you! You were right on target!

  30. Kudos on that with a Dell Latitude E5450, that saved us a lot of time….

  31. same solution for Dell Precision 7510 on Windows 7

  32. same solution for Dell T20 on Windows 10 Pro x64

  33. Same solution for E7450, thank you 🙂

  34. Many thanks it works for Latitude E5450

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