| Previous | Next |
| CO_E_CLASSSTRING | CO_E_APPNOTFOUND |
CO_E_IIDSTRING
Invalid interface string
The native value 0x800401F4 is CO_E_IIDSTRING, unsigned 2147746292 and signed -2147221004. The documented description is “Invalid interface string”. Treat it as evidence that a textual interface identifier cannot be converted into a valid IID; the operation in progress is IIDFromString or configuration-driven interface selection.
Operational meaning
- Associate this result with one exact operation in thread apartment initialization, GUID parsing, class-object discovery, local-server launch, and single-use class-factory registration.
- Confirm that this result came from IIDFromString or configuration-driven interface selection, rather than from cleanup or a wrapper that ran afterward.
Cause model
- It can result when the GUID text is malformed, incomplete, or contains invalid characters.
- It can result when a symbolic interface name is passed where GUID syntax is required.
- It can result when serialization or localization changes the identifier string.
Troubleshooting workflow
- Identify the exact object, method, and lifecycle phase involved in IIDFromString or configuration-driven interface selection.
- Record input length and escaped text without sensitive surrounding configuration.
- Verify that the intended IID comes from a header or type library.
- Test parsing independently from QueryInterface.
What to log
A useful incident records the thread ID and apartment request, CLSID text, IID text, class context, server executable or DLL path, process launch result, class-factory registration flags, timeout, and activation generation.
Correction strategy
Correction: supply a valid GUID string or use the compiled IID constant from the interface definition. Retry condition. Retry only after correcting the text; object replacement cannot make invalid IID syntax parse. Before repeating the operation, balance successful CoInitializeEx calls on the same thread, revoke only class objects actually registered, and determine whether a local server or single-use factory already served a request.
Practical scenario
A script passes “IUnknown” to IIDFromString; exposing the actual IID_IUnknown text or a typed binding removes the ambiguity.
Difference from related HRESULTs
E_NOINTERFACE occurs after a valid IID is requested from an object; it means the IID text itself is invalid.
Developer and administrator guidance
Record the activation phase, parse GUID text before lookup, initialize every participating thread explicitly, and make class-object registration lifetime visible in server state. Regression coverage should include uninitialized and incompatibly initialized threads, malformed CLSID and IID text, missing applications, launch failure, factory-registration races, and single-use consumption.
Verify the registered application and server executable with the supported installation path; thread initialization and class-factory lifetime defects require code fixes rather than registry improvisation.
References
Looking for a different code? Search another status or error code.