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E_SYNCENGINE_FOLDER_INACCESSIBLE
Within Windows cloud-file and sync-engine infrastructure, E_SYNCENGINE_FOLDER_INACCESSIBLE reports that the sync engine lacks effective access to a local folder beneath the sync root. Diagnosis of this result should follow the original owner and generation rather than treating the visible symptom as the cause.
Mechanism behind the code
During a this result investigation, a Windows sync engine coordinates local NTFS objects, provider metadata, remote identifiers, quota and naming rules, placeholder hydration, network authentication, and asynchronous upload or download state. The same Explorer action can cross several of those boundaries, so diagnosis must retain the first failing stage rather than treating every code as a generic connectivity problem.
The interactive user, sync service, and provider process may have different tokens., access can also be denied by sharing mode, encryption, controlled-folder policy, or a stale path after move.
The first owner to inspect is the local sync root, placeholder state, file-system operation, provider request, network exchange, account policy, or remote storage operation that produced the HRESULT.
High-value telemetry
| Capture | Diagnostic value |
|---|---|
| Canonical folder path and file ID for it. | This provides a stable comparison across retries or another machine and helps test the Windows cloud-file and sync-engine infrastructure boundary. |
| Effective process identity for it. | This identifies the exact object or resource generation involved and helps test the Windows cloud-file and sync-engine infrastructure boundary. |
| ACL and integrity level for it. | This places the failure on the lifecycle or transaction timeline and helps test the Windows cloud-file and sync-engine infrastructure boundary. |
| Open flags and sharing failure for it. | This separates caller input from environment and service state and helps test the Windows cloud-file and sync-engine infrastructure boundary. |
Decision table
- Second supported path for the same stable item: for it, a changed result separates retained object, connection, path, host, or device state from the original input. Hold constant: for it, keep account, remote item version, and client build fixed.
- Reduced failing operation: If this result follows the reduced step, the rejecting transition is localized. Hold constant: for it, retain canonical folder path and file id and remove only unrelated work.
- Targeted corrective control: Use this as a diagnostic branch rather than a blanket workaround: test access under the actual engine identity. Hold constant: for it, keep the original this result sample available for the final regression test.
Safe reduction procedure
When it is returned, use a disposable control object, repository copy, file, or device association where the subsystem permits it.
- First: Test access under the actual engine identity.
- Next: Record the immediate Win32 error.
- Then: Correct only the required ACL or ownership.
- Finally: Verify traversal through every parent directory.
Do not erase the distinction
During a it investigation, UNSUPPORTED_FOLDER_NAME is a naming rule; FOLDER_INACCESSIBLE is an effective local-access failure.
Do not grant Everyone full control or take ownership of unrelated trees.
Successful outcome
Verify it with the original scenario, one boundary case, and one deliberate failure; success means the engine can enumerate, create, rename and reopen a test item with least-privilege access.
Technical references
The references below define the API family or storage/protocol behavior used to interpret it.
- Microsoft: Build a Cloud Files sync engine
- Microsoft: Naming files, paths, and namespaces
- Microsoft: Cloud Filter API reference
- Microsoft: Determine cloud placeholder state
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