Magnification API - Sometimes an error occur when the MagSetWindowSource function called

 I am developing a capture application with Magnification API. The program is to capture of both primary and Seconday Screen. Sometimes access violation occur when MagSetWindowSource function called.

1.  The error is 

First-chance exception at 0x7fefeb257c9 in test01.exe: 0xC0000005: Access violation reading location 0x0afff660.

2. My Developing Environment is

OS : windows 7 64bits

Video : NVIDIA Geforce GT 520 , Dual Monitor(Primary 1280x1024, Secondary 1920x1080)

Application : 32bit application.

3. My test code is

if (!MagSetWindowFilterList(hwndMag, MW_FILTERMODE_EXCLUDE, 1, pFilterList))

{  return;

}

RECT sourceRect;

sourceRect.top = 0;

sourceRect.left = m_ScreenX;

sourceRect.right = m_ScreenX + m_ScreenW;

sourceRect.bottom = m_ScreenH;//m_ScreenY;

if (!MagSetWindowSource(hwndMag, sourceRect))// Access violation frequently.  The value of sourceRect is valid.

{

  return;

}

//The reference of this source is http://www.codeproject.com/Articles/607288/Screenshot-using-the-Magnification-library

Please help me. I'dont know why error occur sometimes.

Thank for reading it.