App Hide in Tray Notification Area (next the clock) and WinMessage

Question

Why if my WindowsForm is hidden, the process isn't able to receive wMsg of type 0x4A from other processes ???

If it is Shown, my process can send and receive WMessages toward other applications (locacally)! But if ShowInTaskbar is false, the process can only send WM!!
(MainWindowHandle returns 0 and the message is not reaching)

The final question is following: Is there a way to send and receive messages having the application the Tray Notofication Area (otherwise hidden on the Windows ApplicationBar)??

Excluse for my not perfect english....I hope to have been clean!!

Thanks in advance!

AF.