Create Window failure

static wchar_t g_szClassName[] = L"MyTestApp";
static HINSTANCE g_hInst = NULL;

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
  LPSTR lpCmdLine, int nCmdShow)
{
  WNDCLASSEX WndClass;
  HWND hwnd;
  MSG Msg;

  g_hInst = hInstance;

  WndClass.cbSize        = sizeof(WNDCLASSEX);
  WndClass.style         = NULL;
  WndClass.lpfnWndProc   = WndProc;
  WndClass.cbClsExtra    = 0;
  WndClass.cbWndExtra    = 0;
  WndClass.hInstance     = g_hInst;
  WndClass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
  WndClass.hCursor       = LoadCursor(NULL, IDC_ARROW);
  WndClass.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);
  WndClass.lpszMenuName  = NULL;
  WndClass.lpszClassName = g_szClassName;
  WndClass.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);

  if(!RegisterClassEx(&WndClass))
  {
     MessageBox(0, L"Window Registration Failed!", "Error!",
        MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL);
     return 0;
  }

  hwnd = CreateWindowEx(
     WS_EX_CLIENTEDGE,
     g_szClassName,
     L"",
     WS_OVERLAPPEDWINDOW & ~WS_BORDER,
     CW_USEDEFAULT, CW_USEDEFAULT, 320, 240,
     NULL, NULL, GetModuleHandle(NULL), NULL);

  DWORD x = GetLastError();

  if(hwnd == NULL)
  {
     MessageBox(0, L"Window Creation Failed!", L"Error!",
        MB_ICONEXCLAMATION | MB_OK | MB_SYSTEMMODAL);
     return 0;
  }

  ShowWindow(hwnd, SW_HIDE);
  UpdateWindow(hwnd);


  while(GetMessage(&Msg, NULL, 0, 0))
  {
     TranslateMessage(&Msg);
     DispatchMessage(&Msg);
  }
  return Msg.wParam;
}

In the above code snippet the hwnd is always NULL, Any ideas

Thanks all