bool CALLBACK aaa(HWND h,LPARAM l)
{
  char s[51];
  GetClassName(h,s,50);

TWinControl *a = FindControl(h);

  if(a){                     <----널이므로 넘어감
     ShowMessage(a->Name);
     a->SetFocus();
  }

  Form1->Memo1->Lines->Add(s);

  return true;
}

void __fastcall TForm1::Button3Click(TObject *Sender)
{
        HWND wHandle;
        wHandle = FindWindow(PChar(0), "Form2");   <------ Form2는 다른 프로그램의 캡션

        EnumChildWindows(wHandle,(WNDENUMPROC)aaa,0);
}

위에 처럼인데 널이 들어가는군요