SetWindowLong Hanging

Why SetWindowLong(myForm.hWnd, GWL_HWNDPARENT, parentHwnd)does it freeze?

I can recreate this problem sequentially by following these three steps.

1. Create a .NET Form
2. Initialize the WaitWindow COM object, call ShowWindow on the COM object when passing the .NET form descriptor
3. In VB6, call the SetWindowLong method

C # Windows app (freezes)

private static void Main(string[] args)
{
      Form form = new Form();
      form.Show();

      Interop.WaitWindow waitWindow = new Interop.WaitWindow();
      waitWindow.ShowWindow(form.Handle.ToInt32(), Language.RISEnglish);
}

C # console application (does not freeze)

private static void Main(string[] args)
{
      IntPtr handle = Process.GetCurrentProcess().MainWindowHandle;     

      Interop.WaitWindow waitWindow = new Interop.WaitWindow();
      waitWindow.ShowWindow(handle.ToInt32(), Language.RISEnglish);
}

VB6 code snippet

Public Sub ShowWindow(ByVal parentHwnd As Long, ByVal language As Language)

    SetWindowLong(myForm.hWnd, GWL_HWNDPARENT, parentHwnd)  'Hangs Here
    CenterWindow (parentHwnd)

    myForm.ShowRetrieving (language)
    myForm.Show (vbModal)
End Sub

Really would appreciate your help :)

EDIT

I understand that SetWIndowLong should not be called to change the parent, but I'm trying to understand why it hangs only when using the .NET form descriptor.

EDIT2

, SetWindowLong, . , , VB6 .NET, RPC. , , - .