What does HRESULT 0x800401F9 (CO_E_ERRORINDLL) mean?

CO_E_ERRORINDLL

Meaning

Windows documents CO_E_ERRORINDLL 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.

Likely causes

• Possible cause 1: a dependent DLL cannot be loaded even though the registered server DLL exists.
• Possible cause 2: DllGetClassObject returns a failure for the requested CLSID or IID.
• Possible cause 3: 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 relevant condition is that COM finds the registered in-process module but the DLL fails while loading or supplying the requested class object.

Diagnostic sequence

1. Confirm that the observed path matches this condition: COM finds the registered in-process module but the DLL fails while loading or supplying the requested class object.

Evidence to collect

• Capture 1: Windows loader events, dependency names and native status from the first load attempt.
• Capture 2: the registered DLL path, file version, signature and process architecture.
• Capture 3: the exact result of class-factory acquisition before a wrapper substitutes it.

Correct handling and retry

• Corrective action 1: fix the missing dependency, binary incompatibility or class-factory implementation.
• Corrective action 2: keep DllMain minimal and move recoverable initialization out of loader lock.
• Corrective action 3: redeploy the module using the supported installer rather than manual registration experiments.

Retry guidance. Retry after the loader or class-factory cause is corrected; unloading and immediately loading the identical broken module is not a recovery strategy. When retrying, avoid launch duplicate servers, reuse stale proxies or repeat an activation whose side effects are unknown.

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.

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.

Developer and operational guidance

Official Microsoft references

• Microsoft: generic COM error codes
• Microsoft: CoGetClassObject
• Microsoft: CoCreateInstance