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RPC_E_CANTCALLOUT_AGAIN
Second outgoing call is not allowed on the same DDE channel
RPC_E_CANTCALLOUT_AGAIN is HRESULT 2147549201 (0x80010011) from winerror.h. AllStat describes it as “There is no second outgoing call on same channel in DDE conversation.” In the COM/RPC call control, message filtering, apartment routing, marshaling, security negotiation, or remote object lifetime, the code identifies a specific failure boundary and should not be replaced by a generic COM exception.
Telemetry should preserve this result as a separate outcome rather than merging it with unrelated COM or WinRT failures.
Decisive interpretation boundary
Before choosing recovery, verify that the active conversation, current outbound call, callback stack, and channel ownership are known. That boundary prevents this result from being misclassified as corruption, network failure, or a reason for an unsafe automatic retry.
Also confirm that all observed objects, tokens, buffers, proxies, metadata files, or ACLs belong to the current operation generation and were not retained from an earlier attempt.
Where it is encountered
- This result can be returned during cross-apartment or cross-process COM method invocation and activation. Record the interface, method, component version, thread, apartment, process, and correlation ID.
- This result can be returned during STA message filtering, reentrancy, call cancellation, timeout, or retry handling.
- It can be returned during DCOM security initialization, proxy/stub marshaling, OBJREF processing, and server object lifetime.
The immediate focus for it is legacy OLE/DDE call control where code attempts a nested second outbound call on a channel already servicing one conversation. Keep it attached to that operation; the same numeric severity outside the owning API does not supply enough context.
Correct handling and recovery
Return from the current call before issuing another, queue the follow-up operation, and remove reentrant DDE or OLE automation from callbacks.
An unchanged retry loop for it can duplicate effects, deepen reentrancy, or hide an invalid lifetime transition.
Difference from nearby HRESULTs
It is channel-specific nested call prevention; RPC_E_CANTCALLOUT_ININPUTSYNCCALL concerns outgoing COM calls during input-synchronous dispatch.
Merging it with the neighboring HRESULT would choose the wrong retry, recreation, authorization, or cleanup path.
Lifetime, retry, and cleanup rules
After it, determine whether the current object, interface pointer, call context, token, stream, metadata reader, asynchronous operation, or access-control instance remains valid. Release only resources owned by the failing attempt, cancel callbacks through their documented mechanism, and avoid double close, double commit, repeated activation, or replay of a non-idempotent remote method.
The retry policy for it should state the trigger, maximum attempts, cancellation owner, and reconciliation step for effects that may have completed elsewhere.
Developer and administrator guidance
When it crosses native, managed, scripting, RPC, or WinRT projection boundaries, preserve the unsigned 32-bit HRESULT. Unit tests for it should assert the code-specific postcondition and resource ownership, not merely that an exception was thrown.
Document the owner of the boundary so future occurrences can be correlated across client, proxy, server, package, and security logs. Define who owns retry, cancellation, cleanup, policy changes, package repair, and user-facing messaging for it.
Practical scenario
An OLE container receives a DDE callback and immediately issues another command on the same conversation. It queues the command until the first exchange completes.
A regression test should reproduce it, assert the raw HRESULT and all relevant outputs, then correct only the decisive condition and verify the intended success or neighboring failure result.
References
- Microsoft: COM RPC error codes
- Microsoft: IMessageFilter
- Microsoft: RetryRejectedCall
- Microsoft: CoInitialize
- Microsoft: CoInitializeSecurity
- Microsoft: marshaling rules
- Microsoft: HRESULT values
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