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POActiveX control cannot be instantiated because thread is in a single-threaded apartment. Happens after waking PC from sleep
 

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  1. POActiveX control cannot be instantiated because thread is in a single-threaded apartment. Happens after waking PC from sleep
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    <p>I am working on a VOIP client (Window's form) that opens a browser window (ExtendedWebBrowser) when a call is made or received. Normally it works fine but if the computer is put into sleep mode and then woken the program will crash with the following error:</p> <pre><code>"System.Threading.ThreadStateException crossed a native/managed boundary Message=ActiveX control '8856f961-340a-11d0-a96b-00c04fd705a2' cannot be instantiated because the current thread is not in a single-threaded apartment." </code></pre> <p>I have tried setting threads started in the code with <code>thread.SetApartmentState(ApartmentState.STA)</code> but I am getting the same result. Also, I do have <code>[STAThread]</code> before the <code>main()</code> function. Now I am wondering if it has more to do with a thread not terminating correctly when the computer is put to sleep but I'm not sure. My background is in C++ and DirectX, this is the first Windows form I've worked on so any help would be appreciated.</p> <p><strong>Followup:</strong> I was able to resolve this issue after discovering that after resuming the program was being started on a worker thread instead of the main thread. More information can be read here: <a href="https://stackoverflow.com/questions/10608551/sleepsuspend-and-resuming-windows-form-starts-program-on-worker-thread-instead">Sleep(suspend) and Resuming windows form starts program on worker thread instead of main thread</a></p>
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      1. POActiveX control cannot be instantiated because thread is in a single-threaded apartment. Happens after waking PC from sleep
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    1. COThis is typically induced by a problem with the startup of your program. Remove any custom splashscreen you made and make sure the very first window that is created is initialized on the main thread. This ensures that the SystemEvents class is properly initialized.
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    2. COHi Hans, thank you for the reply. The first window created is initialized on the main thread. However, the first/main form is not the one that errors. The browser window that is opened by the main form is the one that is giving me the error. Additionally, I believe it's important to note that the error only happens after the computer is put into sleep mode and then woken. OnPowerChange the forms are closed and on resume the forms run again like they do on the initial load.
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    3. COWell, unclear but a browser would certainly generate this kind of error. Note how your question title is wrong, it complains because it is **not** being created on an STA thread. No idea what OnPowerChange might be but indications are that whatever event you use is running on the wrong thread and thus triggering the complaint.
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