[Client] "Trying to open League in an illegal way"

This was a problem for me during 5.4/5.5. I'm not sure if it has happened to anybody else, or just me, and I haven't yet tested this on 5.6.

However, sometimes (about 25% of my games) when I Alt+Tab out of the loading screen after Champion Select to browse the net, I physically cannot Tab back into the game. I can click the icon all day and nothing happens, and when I right click the Taskbar icon and click "Open Window," I get a warning message telling me I am trying to open League in an illegal way. I can't close League either because apparently that's illegal as well.

The result is me having to open my Task Manager and force the game window to close, which pops the client back up telling me the game has crashed and to reconnect.

For about the next two or so minutes, any time I click reconnect, it tells me it can't find my network. It's not the firewall problem, it just says to check my internet connection. I can load back in the game usually within 30 seconds of everybody else getting in.

I'm running on Windows 7.

Repro steps (may or may not work):

1. End champion select
2. Immediately Alt+Tab out into another window when the loading screen shows up
3. A minute or so later try to click the Taskbar icon to open the game window
4.