ADO连接数据库有关问题

ADO连接数据库问题
我学习用ADO连接数据库，在连接时可以正常连接，但是在查询表的时候却不能正常Open，
recPtr-> Open(strSQL.AllocSysString(),  
pApp-> m_pConnection.GetInterfacePtr(),
adOpenDynamic,
adLockOptimistic,
adCmdText);
经过调试，发现pApp-> m_pConnection.GetInterfacePtr()的值为NULL所以来导致的错误，但是去不清楚为什么它的值会是空。
我使用的单文档程序，在APP类中连接的数据库：
bool   CLiCaiApp::ConnectionDb()
{
m_pConnection.CreateInstance(_uuidof(Connection));
CString   strSQL;
strSQL   =   "Provider=Microsoft.Jet.OLEDB.4.0;Data   Source=LiCaiDB.mdb ";
try
{
m_pConnection-> Open((_bstr_t)strSQL, " ", " ",adModeUnknown);
}
catch   (_com_error   e)
{
CString   strError;
strError.Format( "打开连接发生异常。%s ",e.ErrorMessage());
AfxMessageBox(strError);
return   FALSE;
}
return   TRUE;
}


BOOL   CLiCaiApp::InitInstance()
{
AfxEnableControlContainer();
//初始化OLE   DLLS
if(!AfxOleInit())
{
AfxMessageBox( "初始化OLE　DLL失败。 ");
return   FALSE;
}
//   Standard   initialization
//   If   you   are   not   using   these   features   and   wish   to   reduce   the   size
//     of   your   final   executable,   you   should   remove   from   the   following
//     the   specific   initialization   routines   you   do   not   need.

#ifdef   _AFXDLL
Enable3dControls(); //   Call   this   when   using   MFC   in   a   shared   DLL
#else
Enable3dControlsStatic(); //   Call   this   when   linking   to   MFC   statically
#endif

//   Change   the   registry   key   under   which   our   settings   are   stored.
//   TODO:   You   should   modify   this   string   to   be   something   appropriate
//   such   as   the   name   of   your   company   or   organization.
SetRegistryKey(_T( "Local   AppWizard-Generated   Applications "));

LoadStdProfileSettings();     //   Load   standard   INI   file   options   (including   MRU)

//   Register   the   application 's   document   templates.     Document   templates
//     serve   as   the   connection   between   documents,   frame   windows   and   views.

CSingleDocTemplate*   pDocTemplate;
pDocTemplate   =   new   CSingleDocTemplate(
IDR_MAINFRAME,
RUNTIME_CLASS(CLiCaiDoc),
RUNTIME_CLASS(CMainFrame),               //   main   SDI   frame   window
RUNTIME_CLASS(CLiCaiView));
AddDocTemplate(pDocTemplate);

//   Parse   command   line   for   standard   shell   commands,   DDE,   file   open
CCommandLineInfo   cmdInfo;
ParseCommandLine(cmdInfo);
//   Dispatch   commands   specified   on   the   command   line
if   (!ProcessShellCommand(cmdInfo))
return   FALSE;
if   (!ConnectionDb())
{
AfxMessageBox( "连接数据库失败。 ");
// return   FALSE;
}
//   The   one   and   only   window   has   been   initialized,   so   show   and   update   it.