How to Fix APC INDEX MISMATCH BSOD Error

According to Microsoft’s official documentation, the bug check error APC INDEX MISMATCH indicates that there has been a mismatch in the asynchronous procedure calls (APC) state index. APC is a special function that executes asynchronously.

This means that a driver or system file has a mismatched sequence of calls to disable and re-enable APCs. Some common solutions to the issue could be a driver update or scanning the system files. However, there are multiple other reasons the PC might run into mismatched APC index errors.

This article explains a few causes that might result in the blue screen, along with possible solutions to fix the issue. So without further delay, let us get into it.

What Causes APC INDEX MISMATCH Blue Screen Error?

How to fix APC INDEX MISMATCH Blue Screen error?

Before we begin, we will perform some troubleshooting steps. These methods will not fix the problem per se but will give you a detailed review of what may be causing the blue screen issue. 

If your PC only boots into the Startup repair menu, you may need to boot into safe mode to perform some of the steps explained below. To boot into safe mode from the Startup Repair Menu.

1. Click on Advanced options.
   
2. Navigate to Troubleshoot > Advanced Options.
3. Select Startup Settings.
   
4. Click on Restart.
5. After the restart, Click F5 to Enable safe mode with Networking. The PC will now boot into safe mode.
   

Check Event Viewer

The event viewer holds the record of everything that happens in a system. Using this special utility, we can determine the reason behind the BSOD. You can also check events right before the blue screen to know what caused the error.

To access and check the Event Viewer, follow the steps mentioned below.

1. Press the Windows + R key to open Run.
2. Type eventvwr and press Enter open the Event Viewer window.
3. On the left panel, expand Windows Logs and click on System.
4. Now on the center panel, you can see all the records of system events.
   
5. You can check Source or the Event ID to locate the blue screen error. The source named BugCheck with Event ID 1001 is the BSOD.
6. To filter BSOD events, click on Filter Current Log.
   
7. Here, set Event sources as Bug check and <All Event IDs> as 1001.
   
8. Click OK to see all the BSOD event in the event viewer.

Now, check the events near the BSOD to determine the exact cause of the issue. Another method to check the reason behind the BSOD is by from DUMP files. Dump files contain a snapshot of information related to specific crash.

Uninstall DisplayLink

DisplayLink application in your PC might be the reason you are getting APC INDEX MISMATCH BSOD error on your PC. A lot of DisplayLink users in different Q/A forum reported that uninstalling DisplayLink fixed the index mismatch blue screen.

If you are have DisplayLink installed in your PC, try removing it.

1. Press the Windows + R key to open Run.
2. Type appwiz.cpl and press enter to open Program and Feature.
3. Select DisplayLink and click on Uninstall.
   
4. Restart your PC to check if the system enters BSOD.

You can also try downloading and reinstalling the application from DisplayLink official website.

Perform Startup Repair

Startup repair tries to fix common issues with Windows that may be stopping the OS from booting. Even though this is very rare, sometimes the system gets stuck on boot loop due to the error. If the system directly boots into the automatic repair menu, you can try running Startup Repair from advanced option.

1. Click on the Advanced options to open Advanced startup options.
   
2. If you want to boot into advanced startup from Windows, click on the Windows key, hold Shift key and click on Restart.
3. Click on Troubleshoot > Advanced Options.
4. Here, select Startup Repair.
   

The PC will restart and start the diagnostic process.

Disable Overclock

Although overclocking a system provides a performance boost, it may even make your system unstable. This may result in the system to display a blue screen error. To disable any overclock done to a system, you can try resetting the BIOS. To reset a BIOS,

1. Enter the BIOS by repeatedly pressing the BIOS key during startup. The BIOS key could be any of the function key or the Delete key.
2. Once in BIOS, search for settings named Load Default Options, Reset, Load Default Settings or Load Setup Defaults.
   
3. Save and exit the BIOS.
4. Once the PC restarts, all your BIOS configuration will have reset.

Update Realtek HD Audio Manager

Most Windows discussion forums have also mentioned that users faced APC_INDEX_MISMATCH BSOD error when Realtek HD Audio Manager is enabled on Startup.

Windows have provided a driver update that fixed the issue. Updating Realtek HD Audio Manager driver may fix the BSOD error. Follow the steps mentioned below to update Realtek HD Audio Manager.

1. Go to Realtek HD Audio Manager official website.
2. Select the latest Realtek HD Audio Manager driver. The installation process should now begin.
3. Run the executable file as Administrator to install the Driver.

Perform Clean Boot

Windows disables any unnecessary services except Microsoft services when performing a clean boot. If any services related to a third-party application are causing the APC INDEX MISMATCH BSOD, performing a clean boot should fix the issue. However, if you are in the advanced startup menu, you can also boot into safe mode to load basic drivers.

1. Press the Windows + R key to open Run.
2. Type msconfig and press enter to open System Configurations.
3. Go to the Services Tab.
4. Click on Hide all Microsoft services and click on Disable all.
   
5. Restart your PC to check if the system starts.

If the system starts and functions smoothly, you need to enable all the services one at a time to check the actual service that is causing the issue. Once you find the service, please remove it from the PC.

Repair System Files

System files are responsible for running the entire Windows. It contains crucial OS and driver files that the system needs. If any of these files gets corrupted or damaged, the integrity of the entire OS may be at stake. This may also result in a random APC INDEX MISMATCH blue screen.

Try repairing the system files using the SFC.

1. Press the Windows key + R key to open Run.
2. Type cmd and press Ctrl + Shift + Enter to open Command Prompt as Admin.
3. Type sfc /scannow to run the system file checker. Wait for the process to complete.
   
4. Restart your PC.

Uninstall Windows Update

After a Windows Update named KB5000802 on Windows 10, many users faced the APC_INDEX_MISMATCH blue screen. Windows triggered the bug every time users tried to print using Type 3 drivers. If this is the case for you, we recommend that you uninstall the KB5000802 Windows update.

1. Press the Windows + I key to open Settings.
2. Go to Windows Update > Update history.
   
3. Select Uninstall updates.
   
4. Click on KB5000802 Windows update and select Uninstall.
   
5. Restart your PC once the process is complete.

Update Drivers

A device drivers works as an interface between the OS and it device. It helps the OS communicate with the device. A corrupted or outdated driver may run into several issues. The device may even run into critical issues that may stop important system process, resulting in the BSOD.

Try updating driver to a latest version.

1. Press the Windows + X key to open Device Manager.
2. Expand a section that is listed on the Device Manager.
3. Right-click and select Update driver.
   
4. Update all the drivers to all the devices.

BSOD Troubleshooter

The BSOD troubleshooter scans and changes necessary settings in Windows to fix the blue screen error. However, BSOD troubleshooter utility is only available on Windows 10. But, the option is not available for Windows 11.

To run the BSOD troubleshooter,4

1. Press the Windows + I icon to open Settings.
2. Go to Update and security > Troubleshoot.
3. Now, run the BSOD troubleshooter.
   
4. Restart your PC once the troubleshooting process is complete.

System Restore

System Restore reverts all your computer setting to previous saved state. This saved state is called a restore point. The restore point is like a snap shot of all your computer settings. Now, once the user prompts a system restore, all the PC’s current settings will be back to its previous state.

Performing a System restore will not delete any files and folders. However, it will remove any application installed after a restore point.

However, before we start, you need a restore point set to before the blue screen started.

1. Press the Windows + R key to open Run.
2. Type rstrui to open System Restore.
3. Click on Next, and select a restore point.
   
4. Click on Next and then select Finish
5. The PC will now reboot reverting back to the restore point.