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| RPC_E_INVALID_DATAPACKET | RPC_E_CLIENT_CANTMARSHAL_DATA |
RPC_E_CANTTRANSMIT_CALL
RPC_E_CANTTRANSMIT_CALL means that COM could not send a call because the relevant message queue remained full after COM yielded. A blocked or overloaded apartment thread is a common contributing condition.
How to investigate
- Inspect whether an STA thread is blocked without dispatching messages.
- Look for synchronous work, long UI handlers, or recursion that prevents the apartment from processing COM traffic.
- Reduce call bursts and avoid sending repeated work to a server that is already unable to drain requests.
The correct fix is to restore progress in the receiving apartment or reduce the backlog, not to spin-retry at full rate.
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