SetWindowsHookEx()

I am developing a program that monitors keyboard and mouse activity independently of screen saver routines. I am trying to do this via the journal record hook. My program compiles okay, but I get a "this program has performed an illegal operation" whenever I try to run it (in or out of MFC Development Studio). According to the MFC documentation, a Win32 journal record hook does not need to have a separate DLL for its hook procedure. My code is structured as follows in the MyApp.cpp file:

BOOL CMyApp::InitInstance()
{
      // MFC's generated stuff
      ....
      ....

      // Initialize my variables to be used
        // in the journal proc, OnIdle()
      m_IdleFileName = "c:\mydir\Myfile.dat";
      m_InIdle = FALSE;
      m_IdleCount = 0;
      m_IdleOffset = 15;

      // Set the journal record hook
      m_Hook = SetWindowsHookEx(WH_JOURNALRECORD,
                    JnlRecProc, NULL, 0);
      if(m_Hook == NULL)
      {
           AfxMessageBox("Initialization error");
           return FALSE;
      }

      return TRUE;
}

/* Idle Time Procedure (Assumption: This is called whenever the program has an empty queue -- When there is no  journal recording. */

BOOL CMyApp::OnIdle(long lcount)
{
      // Get the current time
      m_Now = CTime::GetCurrentTime();

      // On the first call, set the idle flag
        // and get ready to count
      if(lcount == 1)
      {
           m_InIdle = TRUE;
           m_IdleCount = 0;
      }
      else
      {
           m_MinutesElapsed = m_Now - m_LastActivity;
           m_IdleCount =
                      m_MinutesElapsed.GetTotalMinutes();
      }
      return CWinApp::OnIdle(lcount);
}

// Journal Record Procedure
LRESULT CALLBACK CMyApp::JnlRecProc(int ncode,
          WPARAM wparam, LPARAM lparam)
{
      switch(ncode) {
      case HC_ACTION:
          m_LastActivity = CTime::GetCurrentTime();

          // if idle time processing has taken place,
            // save the idle count
          if(m_InIdle)
         {
               if(m_IdleCount > m_IdleOffset)
                    m_IdleCount -= m_IdleOffset;
               else
                   m_IdleCount = 0;

            // Read accumulated idle time from file
            if((fp = fopen(m_IdleFileName, "r")) != NULL)
              {
               if(fread(&m_IdleTime, sizeof m_IdleTime,
                            1, fp) != 1)
                    m_IdleTime = m_IdleCount;
               else
                    m_IdleTime += m_IdleCount;
               fclose(fp);
               }
              else
               m_IdleTime = m_IdleCount;

             // Write new value to file
            if((fp = fopen(m_IdleFileName, "w")) != NULL)
            {
            m_Result = fwrite(&m_IdleTime,
                      sizeof m_IdleTime, 1, fp);
            fclose(fp);
            }

           // Reset flag m_InIdle
          m_InIdle = FALSE;
      }
      break;

        case HC_SYSMODALON:
        case HC_SYSMODALOFF:
      break;

         default:
                 break;
      }
 
     return(CallNextHookEx(m_Hook, ncode, wparam, lparam);
}
      

When I try to debug this, my computer locks up. It appears that the breakdown is occurring within the journal record procedure (and not when the hook is being set).

Can anyone give me a clue as to what is happening here?

Thanks!