程序调试提示“Access Violation”

我用VC写了个在实验数据中寻找需要的数值，每个实验文件中有2034个数据，其中波长和强度值一一对应。主要代码如下：

void CFindPeakDlg::OnBegin()
{
  // TODO: Add your control notification handler code here

    CFileDialog openPre(true,"*.ROH",NULL,OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT|OFN_ALLOWMULTISELECT,
    "待处理文件(*.ROH)|*.ROH|所有文件(*.*)|*.*||");
    DWORD MAXFILE = 256000; //设置缓冲区，
    openPre.m_ofn.nMaxFile = MAXFILE;
    char* pc = new char[MAXFILE];
    openPre.m_ofn.lpstrFile = pc;
    openPre.m_ofn.lpstrFile[0]=NULL;

    int index1=0,x=0;//文件数量统计

      if(openPre.DoModal()==IDOK)
{
//启动EXCEL服务器，设置初始属性
    _Application app;
    Workbooks books;
    _Workbook book;
    Sheets sheets;
    _Worksheet sheet;
      Range range; 
    LPDISPATCH lpDisp;
    COleVariant covOptional((long)DISP_E_PARAMNOTFOUND, VT_ERROR);

    //Create Excel server (start Excel)
    if(!app.CreateDispatch("Excel.Application"))
{
    AfxMessageBox("Can't start Excel serve