APC_INDEX_MISMATCH (stop code 0x00000001) is a driver bookkeeping error: a kernel routine entered or exited with the wrong count of pending asynchronous procedure calls, and Windows crashed rather than continue in an inconsistent state. On Windows 11 24H2 specifically, this spiked because the update tightened kernel behavior and exposed latent bugs in older drivers.

The fix is almost always driver-focused: find the offender, update or remove it. Work through these in order. For general crash diagnosis skills, our blue screen guide covers reading dump files.

Why this happens

  • Outdated drivers on 24H2. Drivers written for older builds break under 24H2’s kernel changes.
  • Realtek audio driver bugs. A notorious trigger for this exact stop code.
  • Graphics driver conflicts. Display drivers mismanaging APC state.
  • Corrupted system files. Damage to kernel files like win32kfull.sys.
  • Third-party antivirus filter drivers. Security software hooking file I/O at the wrong level.
  • Faulty RAM. Memory corruption can garble the APC bookkeeping.
  • Overclocked or unstable hardware. Timing-sensitive bugs surface under 24H2’s stricter kernel.

How to fix it

Work through these in order — note any named file on the blue screen.

Fix 1: Identify the driver from the crash

Get the name before you change anything.

  1. Note any .sys file named on the blue screen (common: win32kfull.sys, rtkvhd64.sys, fltmgr.sys).
  2. Boot into Safe Mode if needed (interrupt boot 2-3 times for WinRE, then Troubleshoot > Advanced options > Startup Settings > Restart, press 4).
  3. Open Event Viewer > Windows Logs > System and find BugCheck entries with the stop code 0x1.
  4. Check C:\Windows\Minidump for recent dump files.
  5. rtkvhd64.sys = Realtek audio, win32kfull.sys = graphics subsystem (suspect GPU driver), fltmgr.sys = file-system filter (suspect antivirus or disk tools).
  6. With the suspect identified, jump to the targeted fix below.

Fix 2: Update or reinstall the Realtek audio driver

The single most common fix for this stop code.

  1. Open Device Manager (Win + X > Device Manager).
  2. Expand Sound, video and game controllers, right-click Realtek Audio, and choose Uninstall device. Tick Attempt to remove the driver for this device if offered.
  3. Restart — Windows installs a generic audio driver.
  4. Test for a day. If crashes stop, the Realtek driver was the cause.
  5. Then install the latest Realtek driver from your laptop maker’s support site (not a random driver site).
  6. If the newest Realtek driver crashes again, stay on the generic Windows driver — you lose some audio enhancements but gain stability.

Fix 3: Clean-reinstall the graphics driver

For crashes naming win32kfull.sys or happening during display changes.

  1. Download DDU (Display Driver Uninstaller) and the latest GPU driver from NVIDIA or Intel .
  2. Disconnect from the internet.
  3. Boot into Safe Mode (Settings > System > Recovery > Advanced startup > Restart now, then Troubleshoot > Advanced options > Startup Settings > Restart, press 4).
  4. Run DDU, choose Clean and restart.
  5. Install the downloaded driver (choose clean/custom install if offered).
  6. Reconnect, restart, and test — especially the scenarios that crashed before (wake from sleep, external monitor, gaming).

Fix 4: Temporarily remove third-party antivirus

Filter drivers are a classic APC mismatch source.

  1. Uninstall your third-party antivirus from Settings > Apps > Installed apps (save your license key).
  2. Restart — Windows Defender takes over automatically.
  3. Use the system for a couple of days, including sleep/wake cycles which often trigger this crash.
  4. If crashes stop, reinstall the latest version of your antivirus from the vendor’s site — or stay with Defender, which is fully 24H2-compatible.
  5. Never run with no protection at all.
  6. This step also applies to third-party disk tools and encryption software with filter drivers.

Fix 5: Repair system files

Fix corruption in the kernel files involved.

  1. Open an elevated terminal: right-click Start > Terminal (Admin).
  2. Run: DISM /Online /Cleanup-Image /RestoreHealth
  3. Then: sfc /scannow
  4. Restart.
  5. If SFC repaired win32kfull.sys or related files, that was likely your crash source.
  6. Check support.microsoft.com for any 24H2-specific servicing stack updates you might be missing.

Fix 6: Update everything for 24H2 compatibility

Bring the whole driver stack up to the new build.

  1. Open Settings > Windows Update and install all updates.
  2. Check Advanced options > Optional updates for driver updates and install them.
  3. Visit your laptop maker’s support site and install any drivers marked 24H2-compatible — chipset and BIOS especially.
  4. Update the BIOS if a newer version exists (charger connected, don’t interrupt).
  5. After all updates, restart and test the previously-crashing scenarios.
  6. If a specific optional driver update coincides with new crashes, roll it back immediately — 24H2’s driver catalog isn’t perfect either.

Fix 7: Test RAM and consider rolling back

Cover the hardware angle and the escape hatch.

  1. Press Win + R, type mdsched.exe, and choose Restart now and check for problems.
  2. Check results under Event Viewer > Windows Logs > System > MemoryDiagnostics-Results.
  3. If RAM is clean and crashes persist across all driver fixes, consider rolling back: Settings > System > Recovery > Go back (available ~10 days after the 24H2 upgrade).
  4. Before rolling back, export your minidumps from C:\Windows\Minidump — useful if you report the bug.
  5. After rolling back to 23H2, pause feature updates while you wait for driver vendors to catch up.
  6. For persistent crashes with no driver ever named, our MEMORY_MANAGEMENT guide covers deeper memory diagnosis.

Closing

APC_INDEX_MISMATCH on 24H2 is overwhelmingly a driver-compatibility story, with Realtek audio leading the suspect list. Work from the named file outward, don’t be afraid to run the generic Windows audio driver, and keep everything 24H2-current. The 24H2 kernel is stricter than its predecessors — which is good for long-term stability, once your drivers catch up.

Frequently asked questions

What does APC_INDEX_MISMATCH mean?
Stop code 0x00000001: a driver or system routine mismatched the count of asynchronous procedure calls when entering or leaving a critical region. In plain terms, a driver did its bookkeeping wrong — most often a file-system, audio, or graphics driver.
Why is this common on Windows 11 24H2 specifically?
24H2 changed kernel timing and driver validation, which exposed bugs in older drivers that worked fine on 23H2. Drivers not yet updated for 24H2 — especially Realtek audio and older storage drivers — are frequent triggers.
The blue screen names win32kfull.sys. What do I do?
That’s a Windows graphics subsystem file, which usually means a third-party graphics or display driver provoked it rather than Windows itself being broken. Clean-reinstall your GPU driver first, then run SFC to verify system files.
Can I just roll back to 23H2?
Within 10 days of upgrading, yes: Settings > System > Recovery > Go back. After that window, you’d need a clean install of 23H2. But fixing the driver is usually faster and keeps you on the supported build.