Fix APC Index Mismatch BSOD While Printing in Windows 10

If you get an APC Index Mismatch blue screen while printing in Windows 10, the fix is usually to update or reinstall your printer driver, or to disable the problematic driver’s memory integrity setting. This error is a bug check (0x00000001) that occurs when a kernel-mode driver calls KeAcquireSpinLock or KeReleaseSpinLock with mismatched IRQL levels, often triggered by an outdated or incompatible printer driver. Below are the exact steps to resolve it, plus background on why it happens and how to prevent it.

What Causes the APC Index Mismatch BSOD

The APC Index Mismatch error is a Windows bug check that indicates a driver attempted to release a spin lock it didn’t own, or called a synchronization routine at the wrong IRQL (Interrupt Request Level). When you print, the printer driver (often a kernel-mode driver like a USB or network printer driver) runs in the context of the print spooler. If the driver has a bug—such as a race condition or improper lock handling—it can trigger this BSOD. Common triggers include:

Outdated or corrupted printer drivers
Conflicts with third-party security software that hooks into the print stack
Windows updates that change kernel interfaces, breaking older drivers
Faulty USB or network printer connections

Step-by-Step Fix: Update or Reinstall the Printer Driver

The most direct fix is to replace the problematic driver. Here’s how to do it safely:

Press Windows + X and select Device Manager.
Expand Print queues (or Printers), right-click your printer, and choose Uninstall device. Check Delete the driver software for this device if available.
Restart your PC. Windows will attempt to reinstall the driver automatically, but it may install the same buggy version.
Go to your printer manufacturer’s support website, download the latest driver for your exact model and Windows 10 version (32-bit or 64-bit), and install it.
After installation, restart again and test printing.

If the BSOD persists, try using the generic Microsoft driver instead: in Device Manager, right-click the printer, select Update driver > Browse my computer > Let me pick from a list, and choose Microsoft Software Printer Driver (or Microsoft IPP Class Driver). This often bypasses the buggy vendor driver.

Disable Memory Integrity (If Driver Is Incompatible)

Windows 10’s Memory Integrity feature (part of Core Isolation) can cause the APC Index Mismatch BSOD if a printer driver isn’t compatible with it. Disabling it may stop the crashes, but note that it reduces security against kernel-level attacks. To disable:

Open Windows Security > Device security > Core isolation details.
Toggle Memory integrity to Off.
Restart your PC.

If the BSOD stops, you’ll need to decide between keeping the feature off or finding a driver that supports it. Many vendors have updated drivers, so try updating first.

Check for Conflicting Software and Services

Third-party antivirus or printer management software can interfere with the print spooler and trigger the error. To isolate:

Run sfc /scannow in an elevated Command Prompt to repair system files.
Run DISM /Online /Cleanup-Image /RestoreHealth to fix Windows image issues.
Boot into Safe Mode and try printing. If no BSOD occurs, a third-party driver or service is the culprit.
Temporarily disable your antivirus (if it has a print filter) and test.

Use the Print Spooler Troubleshooter and Reset

The print spooler service can get stuck with corrupted files. Resetting it often clears the issue:

Press Windows + R, type services.msc, and press Enter.
Right-click Print Spooler and select Stop.
Navigate to C:\Windows\System32\spool\PRINTERS and delete all files inside (this clears queued print jobs).
Go back to Services, right-click Print Spooler, and select Start.

You can also run the built-in troubleshooter: Settings > Update & Security > Troubleshoot > Additional troubleshooters > Printer.

When to Use Driver Verifier (Advanced)

If the BSOD still occurs, you can use Driver Verifier to identify the exact faulty driver. This is an advanced tool that stresses drivers to find bugs, and it will likely cause more BSODs—but the resulting dump file will name the driver. Use it only if you are comfortable analyzing crash dumps:

Open an elevated Command Prompt and type verifier.
Select Create standard settings > Automatically select unsigned drivers (or choose specific drivers).
Restart and reproduce the printing issue. The BSOD will point to the offending driver.
After capturing the info, disable Driver Verifier by running verifier /reset in safe mode.

Frequently Asked Questions

Can a USB cable cause APC Index Mismatch?

Yes, a faulty USB cable or port can cause intermittent communication errors that trigger the driver bug. Try a different cable, port, or a wired network connection to rule this out.

Will updating Windows fix the BSOD?

Sometimes. Windows updates often include driver fixes and kernel changes that can resolve the mismatch. Ensure you have all pending updates installed, but also check for driver-specific updates from the manufacturer.

Is APC Index Mismatch dangerous for my data?

The BSOD itself doesn’t corrupt data, but if it happens during printing, the print job may be lost. Frequent BSODs can cause file system issues if they occur during disk writes, so it’s best to fix it promptly.

Why does the BSOD only happen when printing?

Because the printer driver is only loaded and exercised during print operations. The bug in the driver’s spin lock handling only manifests when the driver is actively processing print data.

Can I just disable the printer driver to stop the BSOD?

Disabling the printer driver will stop the BSOD but also stop printing. A better approach is to uninstall and reinstall with the latest version, or use the Microsoft generic driver as a temporary workaround.

Does this error occur on Windows 11 too?

Yes, the APC Index Mismatch bug check exists in Windows 11 as well. The same troubleshooting steps apply, though the Settings paths may differ slightly.

General steps for current mainstream versions; menus can differ by device and version. See the disclaimer or report an error.

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