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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
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.
High-value telemetry
- Canonical folder path and file ID.
- Effective process identity.
- ACL and integrity level.
- Open flags and sharing failure.
Decision table
- Second supported path for the same stable item: a changed result separates retained object, connection, path, host, or device state from the original input. Hold constant: 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: 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: keep the original failing sample available for the final regression test.
Safe reduction procedure
Use a disposable control object, repository copy, file, or device association where the subsystem permits that safely.
- 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 an 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
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