ExitWindowsEx fails when Windows desktop Locked

Create a form (I'm using .NET 2.0) with a button click event:

{
Thread.Sleep(3000);
ExitWindowsEx(0,0); // shutdown
}

Hit the button, press Left-WindowsKey + L to lock the desktop. The shutdown fails.

ExitWindowsEx returns 1 (Succes开发者_开发问答s).

Why does this API fail, and what else might fail when the desktop is locked?

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The API fails because you're on a different desktop, and are therefore no longer the interactive user. From MSDN:

Therefore, if you are not the interactive user, the function can succeed without actually shutting down the computer. If you are not the interactive user, use the InitiateSystemShutdown or InitiateSystemShutdownEx function.

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use http://msdn.microsoft.com/en-us/library/aa376873(VS.85).aspx. (InitiateSystemShutdown). ExitWindowsEx is 'interactive' logout.