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While researching this issue, I found multiple mentions of the following scenario online, invariably as unanswered questions on programming forums. I hope that posting this here will at least serve to document my findings. First, the symptom: While running pretty standard code that uses waveOutWrite() to output PCM audio, I sometimes get this when running under the debugger: ntdll.dll!_DbgBreakPoint@0() ntdll.dll!_RtlpBreakPointHeap@4() + 0x28 bytes ntdll.dll!_RtlpValidateHeapEntry@12() + 0x113 bytes ntdll.dll!_RtlDebugGetUserInfoHeap@20() + 0x96 bytes ntdll.dll!_RtlGetUserInfoHeap@20() + 0x32743 bytes kernel32.dll!_GlobalHandle@4() + 0x3a bytes wdmaud.drv!_waveCompleteHeader@4() + 0x40 bytes wdmaud.drv!_waveThread@4() + 0x9c bytes kernel32.dll!_BaseThreadStart@8() + 0x37 bytes While the obvious suspect would be a heap corruption somewhere else in the code, I found out that that's not the case. Furthermore, I was able to reproduce this problem using the following code (this is part of a dialog based MFC application:) void CwaveoutDlg::OnBnClickedButton1() { WAVEFORMATEX wfx; wfx.nSamplesPerSec = 44100; /* sample rate */ wfx.wBitsPerSample = 16; /* sample size */ wfx.nChannels = 2; wfx.cbSize = 0; /* size of _extra_ info */ wfx.wFormatTag = WAVE_FORMAT_PCM; wfx.nBlockAlign = (wfx.wBitsPerSample >> 3) * wfx.nChannels; wfx.nAvgBytesPerSec = wfx.nBlockAlign * wfx.nSamplesPerSec; waveOutOpen(&hWaveOut, WAVE_MAPPER, &wfx, (DWORD_PTR)m_hWnd, 0, CALLBACK_WINDOW ); ZeroMemory(&header, sizeof(header)); header.dwBufferLength = 4608; header.lpData = (LPSTR)GlobalLock(GlobalAlloc(GMEM_MOVEABLE | GMEM_SHARE | GMEM_ZEROINIT, 4608)); waveOutPrepareHeader(hWaveOut, &header, sizeof(header)); waveOutWrite(hWaveOut, &

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