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copied!<p>This is a problem that's commonly induced by the SystemEvents class when you have a non-standard way to initialize your user interface. Using threads, specifically. Start your program, Debug + Break All, Debug + Windows + Threads. If you see a thread named ".NET SystemEvents" then you're pretty much guaranteed to get this hang.</p> <p>Some background: the SystemEvent class supports both console mode apps and GUI apps. For the latter, it should fire its event handlers on the UI thread. The very first time one of its events is subscribed, it creates a little invisible helper window to get the system notifications. It can do this two ways, either by creating the window on the calling thread or by starting up a helper thread. It makes the decision based on the value of Thread.GetApartmentState(). If it is STA then it can create the window on the calling thread and all event callbacks can be properly marshaled to that thread.</p> <p>This goes wrong if the <em>first</em> window you create is not created on the UI thread. A splash screen for example. That window may contain controls that are interested in a system event like UserPreferenceChanged so they can properly repaint themselves. It now uses the helper thread and any event will be fired from that helper thread, not the UI thread. Poison to any window that runs on the UI thread. The session switch out of a locked workstation (including the screen saver) is for some mysterious reason very likely to cause deadlock. You may also see an occasional painting mishap, the less nasty result of using windows from the wrong thread.</p> <p>Short from fixing the initialization order, a workaround is to put this in your Main() method, before <em>any</em> windows are created:</p> <pre><code>Microsoft.Win32.SystemEvents.UserPreferenceChanged += delegate { }; </code></pre>

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