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Editorial Team
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Asked: 2026-06-17T21:40:46+00:00

I have replicated this issue in both Project 2010 and 2013. I developed a

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I have replicated this issue in both Project 2010 and 2013.

I developed a VSTO addin, using Visual Studio 2010. In this addin, I have exposed a COMVisible method.

I also have a different (non .NET) application, which then instantiates the Project COM object, searches for my addin and calls the method that I marked as COMVisible.

This causes Project to open a “new” Project file and write something to it.

This non-.NET application, after calling the COM method in my addin, stops execution (without closing MS Project).

I then close the newly created Project (not MS Project, just the file). Everything is fine; however, when I try to close MS Project, it hangs indefinitely. In the Task Manager, it is still shown as “Running” and clicking on the MS Project window brings up a “Switch To”, “Retry”, “Cancel” dialog, informing me that some other application is busy…

Surprisingly, if I choose to NOT close the newly created Project file, and simply close the MS Project window, it closes normally.

What might be going on here?

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1 Answer

  1. Editorial Team

    Ok, after much investigation, I found the answer to the problem. Basically the COM class exposed from my VSTO Addin needs to inherit “StandardOleMarshalObject”.

    The reason for this is because the COM method in my Addin was accessing the Project Object Model on a secondary thread (the thread of the calling application). This is a big no no. Deriving from that class marshals all call on that secondary thread to the primary UI thread, thus fixing the problem.

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