The APC_INDEX_MISMATCH bug check has a value of 0x00000001. The bug check indicates a mismatch in the asynchronous procedure calls (APC) state index.


This article is for programmers. If you're a Microsoft customer and your computer displays a blue screen error code, see Troubleshoot blue screen errors.


Parameter Description
1 The address of the system function (system call) or worker routine.
2 The value of the current thread's ApcStateIndex field.
3 The value of current thread's CombinedApcDisable field. This field consists of two separate 16-bit fields: (Thread >SpecialApcDisable < < 16) | Thread >KernelApcDisable.
4 Call type:
0 - System call
1 - Worker routine


The most common cause of this bug check is when a file system or driver has a mismatched sequence of calls to disable and re-enable APCs. The key data item is the Thread >CombinedApcDisable field. The CombinedApcDisable field consists of two separate 16-bit fields: SpecialApcDisable and KernelApcDisable. A negative value of either field indicates that a driver has disabled special or normal APCs (respectively) without re-enabling them. A positive value indicates that a driver has enabled special or normal APCs too many times.


You can resolve this problem by using WinDbg or by using basic troubleshooting techniques.

Debug by using WinDbg

The !analyze debugger extension displays information about the bug check and can help you determine the root cause.

You can use the !apc extension to display the contents of one or more APCs.

You also can set a breakpoint in the code that precedes this stop code and attempt to single-step forward into the faulting code.

For more information about using WinDbg, see Crash dump analysis using the Windows debuggers (WinDbg).

Debug without using WinDbg

If you aren't equipped to use the Windows debugger to work on this problem:

  • In Event Viewer, check System Log for more error messages that might help you identify the device or driver that's causing this bug check.

  • If a driver is identified in the bug check message, disable the driver or check with the manufacturer for driver updates.

  • Confirm that any new hardware that's installed is compatible with the installed version of Windows. For example, you can get information about required hardware at Windows 10 specifications.

For more general troubleshooting information, see Blue screen data.


This bug check is the result of an internal error in the kernel. This error occurs on exit from a system call. A possible cause for this bug check is a file system or driver that has a mismatched sequence of system calls to enter or leave guarded or critical regions. For example, each call to KeEnterCriticalRegion must have a matching call to KeLeaveCriticalRegion.

If you're developing a driver, you can use Static Driver Verifier, a static analysis tool available in Windows Driver Kit, to detect problems in your code before you ship your driver. Run Static Driver Verifier with the CriticalRegions rule to verify that your source code uses these system calls in correct sequence.

See also

Bug check code reference