RegisterPointerInputTarget return false

Question

Hi I'm trying to upgrade a .Net project running well on Windows7 to Windows8. This program use touch screen capacities.

On my Windows7 project my code in C# works fine and use the following implementation:

    [DllImport("User32")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool RegisterTouchWindow(IntPtr handle, UInt32 flags);

     public AtlEventTouch(IntPtr handle)
    {
        IntPtr hwnd = GetModuleHandle("User32");
        UIntPtr address = GetProcAddress(hwnd, "RegisterTouchWindow");

        if (address != UIntPtr.Zero)
        {
          if (RegisterTouchWindow(handle, 0))                          //<= Here RegisterTouchWindow return true as expected
            _flagTouchCapable = true;                                       // so my flag is set to true
        }
    }

But now with Windows8 I wish to use the new Api function RegisterPointerInputTarget, so I tried this : 

    [DllImport("User32")]
    [return: MarshalAs(UnmanagedType.Bool)]
    private static extern bool RegisterPointerInputTarget(IntPtr handle, PointerInputType flags);

    public AtlEventTouch(IntPtr handle)
    {
        IntPtr hwnd = GetModuleHandle("User32");
        UIntPtr address = GetProcAddress(hwnd, "RegisterPointerInputTarget");

        if (address != UIntPtr.Zero)
        {
          if (RegisterPointerInputTarget(handle, PointerInputType.TOUCH))             //<= Here RegisterPointerInputTarget return FALSE
            _flagTouchCapable = true;                                                                        // so my flag is NOT set to true
        }
    }

   

     public enum PointerInputType
    {

        POINTER = 0x00000001,

        TOUCH = 0x00000002,

        PEN = 0x00000003,

        MOUSE = 0x00000004,

    }

Is it the way I describe the RegisterPointerInputTarget function in my DllImport ?