Skip to content
PCDecoder
0x00000001APC_INDEX_MISMATCHStop codeWidely reported

APC_INDEX_MISMATCH (0x1): what it means and how to fix it

Updated Oct 11, 2026 · Checked against Microsoft documentation · How this page is made

Quick answer

Stop code APC_INDEX_MISMATCH (0x00000001) is a blue screen crash caused by a driver or file system making unbalanced internal calls inside the Windows kernel. Most crashes stem from software that disables background tasks and fails to restore them properly. Start by checking Event Viewer to find and update the driver responsible.

What it means

Windows uses internal mechanisms called Asynchronous Procedure Calls (APCs) to direct tasks to specific processing threads. When a driver or file system component performs critical work, it temporarily disables these calls so its work can proceed without interruption. Once that work finishes, the software must balance the sequence by re-enabling APC execution before returning control to the operating system.

A stop code 0x00000001 indicates that a thread attempted to exit a system call or worker routine with an invalid state index. In simple terms, a driver turned procedure calls off and forgot to turn them back on, or turned them back on too many times. Windows tracks these changes using an internal counter named CombinedApcDisable, which combines two values: SpecialApcDisable and KernelApcDisable. If either value ends up negative, a driver disabled APCs without restoring them. If the value ends up positive, a driver enabled them excessively.

Critical regions and kernel stability

Inside the kernel, routines that enter guarded or critical regions—such as KeEnterCriticalRegion—must be paired with an identical exit call, such as KeLeaveCriticalRegion. When a driver exits a system call while these calls are unbalanced, the operating system detects an internal inconsistency. Letting execution proceed with an incorrect index risks system deadlocks or file system corruption, so Windows stops immediately with a blue screen.

The fault generally lies within third-party driver code or file system filters rather than physical component failure. The stop screen parameters supply technical clues, including the address of the failing system routine, the ApcStateIndex value, the CombinedApcDisable value, and whether the failure occurred during a system call (0) or a worker routine (1).

Common causes

  • A device driver disabled asynchronous procedure calls without properly re-enabling them.
  • A driver re-enabled procedure calls too many times, leaving an invalid positive count in the kernel.
  • A file system filter or driver exited a critical region without a matching leave call.
  • Incompatible newly installed hardware or an outdated third-party driver running on your version of Windows.

How to fix it

Safest and most likely fixes first. Readers' answers to "Did this fix it?" reorder this list over time.

  1. Check the System Log in Event Viewer

    Use this first to see which driver or device triggered the crash before changing system files.

    1. Press Windows Key + X and select Event Viewer.
    2. Expand Windows Logs in the left sidebar and click System.
    3. Look for Error entries timestamped right before or during the crash.
    4. Inspect the General tab of those entries for the names of specific driver files or hardware devices.
    Did this fix it?

  2. Update or disable the faulting driver

    Use this if the blue screen text or Event Viewer points to a specific driver file.

    1. Note the file name of the driver identified in Event Viewer or on the crash screen.
    2. Visit the official website of the component manufacturer to download and install the latest driver update.
    3. If an update is not available, press Windows Key + X and select Device Manager.
    4. Locate the device using that driver, right-click it, and select Disable device to stop the crashes.
    Did this fix it?

  3. Verify hardware compatibility

    Use this if the blue screen started appearing after you installed a new internal or external hardware component.

    1. Disconnect any recently attached external hardware or remove newly installed expansion cards.
    2. Check the hardware manufacturer documentation to confirm full compatibility with your version of Windows.
    3. Restart the PC without the new hardware to see if the system runs stably.
    Did this fix it?

  4. Analyze the crash dump with WinDbg

    Use this advanced step if Windows does not identify the driver on screen and Event Viewer has no clear records.

    1. Install WinDbg from Microsoft.
    2. Launch WinDbg as an administrator and open the dump file located in C:\Windows\Minidump or C:\Windows\MEMORY.DMP.
    3. Enter !analyze -v into the command prompt at the bottom and press Enter.
    4. Examine the output for the failing driver name, or run the !apc extension command to review procedure call states.
    Did this fix it?

Is it just you?

25+ Microsoft Q&A threads discuss this. Most recent activity:

Checked Oct 9, 2026. Refreshed automatically every few days.

Sources

Frequently asked questions

What does APC stand for in Windows?

APC stands for Asynchronous Procedure Call. It is a kernel mechanism that allows Windows to execute routines in the context of a specific thread.

Is APC_INDEX_MISMATCH a hardware failure?

It is almost always caused by software bugs or driver errors inside kernel code, though incompatible newly installed hardware can also trigger it.

What do the four parameters on the crash screen mean?

The parameters indicate the address of the failing routine, the ApcStateIndex value, the CombinedApcDisable counter, and whether the error occurred during a system call (0) or worker routine (1).

More stop codes decoded