WndProc when ShowInTaskBar = false

[Guest]

I have two projects - one in C++ and one in C#. I send win messages from C++
project like
:ostMessage(HWND_BROADCAST, RegisterWindowMessage("MYMSGS"), 0, 0);


and I catch them in C# project by the function

protected override void WndProc(ref Message messg)

My problem is - all works ok untill I set ShowInTaskBar = false. After
ShowInTaskBar = false no one message don't come to WndProc.
Why?

Thanks
Ivana