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CO_E_ERRORINDLL
Meaning and numerical form
CO_E_ERRORINDLL is HRESULT 2147746297 (0x800401F9; signed -2147220999). AllStat records its meaning as “Error in the DLL”. In practical terms, it is returned when COM finds the registered in-process module but the DLL fails while loading or supplying the requested class object.
The severity bit in 0x800401F9 is set, so this result is a failure result rather than a success or informational status. Its facility is 4 (FACILITY_ITF) and its low 16-bit code is 505 (0x01F9). Those fields classify the value but do not identify the component instance, call, object or input that produced it.
Likely causes
- Possible cause 1 for it: a dependent DLL cannot be loaded even though the registered server DLL exists.
- Possible cause 2 for it: DllGetClassObject returns a failure for the requested CLSID or IID.
- Possible cause 3 for it: process initialization, runtime compatibility or module entry-point work fails.
Where the failure belongs
This result belongs to COM activation and object lifetime. COM activation is a sequence rather than one registry lookup: identifier resolution, class registration, module or process start, class-factory publication, marshaling, and object lifetime can fail independently. The decisive condition is this: COM finds the registered in-process module but the DLL fails while loading or supplying the requested class object. Record the first native producer instead of relying only on a framework exception translated several layers later.
Do not infer from this result alone that reinstalling, rebooting or repeating the whole workflow is appropriate. Because it can cross process and language boundaries, its correction depends on the object identity, lifecycle generation, input and state at the first failing call.
Diagnostic sequence
- Capture this result at the first native return and identify the exact object and method.
- Confirm that the observed path matches this the condition: COM finds the registered in-process module but the DLL fails while loading or supplying the requested class object.
- compare the live state with the method contract before changing configuration.
- collect the code-specific evidence listed above and preserve any more specific preceding error.
- change one evidence-backed cause at a time, then repeat the smallest operation that can prove the correction.
- Add a regression check that distinguishes it from the related outcomes described below.
Evidence to collect
A useful it record includes the native API or interface method, component or CLSID, process and thread IDs, architecture, apartment where relevant, operation correlation ID, elapsed time, input identity, and the first state-changing event before failure. When diagnosing it, preserve IErrorInfo, an inner HRESULT, Win32 status, device event or provider message when available.
- Capture 1 for it: Windows loader events, dependency names and native status from the first load attempt.
- Capture 2 for it: the registered DLL path, file version, signature and process architecture.
- Capture 3 for it: the exact result of class-factory acquisition before a wrapper substitutes it.
Telemetry for it should retain types, lengths, hashes, stable opaque identifiers and lifecycle generations while redacting content and credentials. This makes repeated incidents comparable without exposing paths, object identities, user data or credentials.
Correction and retry boundary
- Corrective action 1 for it: fix the missing dependency, binary incompatibility or class-factory implementation.
- Corrective action 2 for it: keep DllMain minimal and move recoverable initialization out of loader lock.
- Corrective action 3 for it: redeploy the module using the supported installer rather than manual registration experiments.
Retry guidance for it. Retry after the loader or class-factory cause is corrected; unloading and immediately loading the identical broken module is not a recovery strategy. A it retry must avoid this hazard: launch duplicate servers, reuse stale proxies or repeat an activation whose side effects are unknown. It must also preserve the evidence needed to locate the original producer of it.
Difference from nearby HRESULTs
CO_E_DLLNOTFOUND points to an absent registered DLL, whereas it is reached after COM has a module path and encounters a DLL-side failure. Keep these outcomes separate in logs, exception mappings, user messages, dashboards and automated retry policy.
Practical scenario
The registered DLL is present, but one of its private runtime dependencies is absent on a clean machine; dependency tracing identifies the real cause behind it. The result scenario narrows the result to a reproducible contract boundary and supplies a concrete before-and-after test.
Developer and operational guidance
Code handling it should log the failed stage before cleanup, keep ownership and lifecycle transitions explicit, and avoid converting every failure into a generic message. Tests for it should cover the primary cause, one adjacent HRESULT and the retry boundary so a future change cannot turn a deterministic contract failure into an uncontrolled loop.
Operational repair for it should use supported product installation, COM registration, activation and class-factory lifetime paths. Avoid unsupported configuration edits or component replacement unless evidence identifies that layer. Retain the original trace and a post-fix trace so the result can be attributed and the change reversed.
Official Microsoft references
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