What does HRESULT 0x80010005 (RPC_E_CANTCALLOUT_INEXTERNALCALL) mean?

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COM blocked a nested outgoing call while code was executing inside a message-filter callback.

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RPC_E_CANTCALLOUT_INASYNCCALL	RPC_E_CONNECTION_TERMINATED

RPC_E_CANTCALLOUT_INEXTERNALCALL

RPC_E_CANTCALLOUT_INEXTERNALCALL means that code attempted an outgoing COM call while COM was invoking a message-filter callback. Such nested calls can cause unsafe reentrancy and are not allowed in that context.

How to correct the callback

Do not invoke COM objects from IMessageFilter methods.
Return the message-filter decision first, then schedule any follow-up work after the callback completes.
Separate retry or UI decisions from the operation that needs to call the server.

A message filter is a control point for COM call handling, not a safe general-purpose place to call into another COM server.

Microsoft: COM documentation

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