MainMenu VK interference

I am starting an application with process.start, and then sending virtual keys to it (VK_RETURN).
It works fine, but if the user opens the main menu while, the program has a brain fart.
I have tried to use API's lockwindowupdate, and blockinput, putfocus, setforegroundwindow, and even allowsetforegroundwindow, to no avail.
With the old vb6 I believe Me.enabled = false works, but not with .NET.

Is there any way to disable, or back out of the mainmenu before sending keys? I also tried setting the focus elsewhere first, so that the menu should hide, but noahha.

This is frustrating!
Sometimes I wonder about the people who developed the software.