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CoInitializeEx function fails after calling the HtmlHelp function on the same thread

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This article discusses an issue where the CoInitializeEx function fails after calling the HtmlHelp function on the same thread.

Applies to:   All supported operating system

Symptoms

If an application calls HtmlHelp before calling CoInitializeEx with the specified COINIT_MULTITHREADED value, CoInitializeEx can return RPC_E_CHANGED_MODE (0x80010106). As a result, the application may crash, hang, or display unexpected behavior.

Cause

If a thread that calls HtmlHelp hasn't been initialized with CoInitialize or CoInitializeEx, HtmlHelp initializes the thread as apartment-threaded with COINIT_APARTMENTTHREADED.

Workaround

To work around the issue and avoid the conflict of COM initialization on a single thread, create a new thread and call HtmlHelp on that thread.