/// The WM_QUIT message indicates a request to terminate an application and is generated when the application calls the PostQuitMessage function. It causes the GetMessage function to return zero.

                        Win32.PostQuitMessage(0);

static extern void PostQuitMessage(int nExitCode);

Public Shared Sub PostQuitMessage( _

MSDN recommends using PostQuitMessage over PostMessage when you want to send WM_QUIT http://msdn.microsoft.com/en-us/library/ms632641%28v=vs.85%29.aspx