How to fix Error 366 on Windows 11

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Windows 11 Error 366: Cloud File Property Checksum Mismatch

Why This Error Happens

Error 366 occurs when the Cloud Filter API (CldFlt.sys) detects that the metadata checksum stored for a placeholder file does not match the checksum computed at read time, indicating the on-disk cloud file property has been corrupted. This typically happens due to abrupt shutdowns, disk errors, or interrupted sync operations that leave the NTFS reparse point data and its associated placeholder metadata in an inconsistent state. Third-party antivirus or backup tools that scan or lock files mid-sync can also corrupt these cloud placeholder attributes.

Step-by-Step Resolution Guide

  1. Pause and restart the sync client (OneDrive, or third-party cloud provider using Cloud Filter API):
  • Right-click the cloud icon in the system tray → Pause syncing → wait 1 minute → Resume syncing.
  1. Run OneDrive’s built-in reset command (fixes corrupted placeholder metadata):
  • Press Win + R, enter:

    %localappdata%\Microsoft\OneDrive\onedrive.exe /reset
  • Wait for the OneDrive icon to disappear and reappear in the taskbar (may take a few minutes). If it doesn’t restart automatically, relaunch it via Win + R → onedrive.exe.
  1. Check disk integrity to rule out underlying corruption:
  • Open Command Prompt as Administrator and run:

    chkdsk C: /f /r
  • Schedule the scan on next restart if prompted, then reboot.
  1. Unpin and re-pin the affected file/folder to force regeneration of the placeholder metadata:
  • Right-click the corrupted file → “Always keep on this device” (to force full download), then toggle back to “Free up space” if desired.
  1. Clear the Cloud Filter cache via PowerShell (if the error persists across multiple files):
  • Run PowerShell as Administrator:
    powershell
    Get-Service CldFlt | Restart-Service -Force
  • Restart the machine afterward to fully reinitialize the filter driver.

Alternative or Verification Steps

  • Verify the fix: Open Event Viewer (eventvwr.msc) → Windows Logs → Application, and confirm Error 366 no longer recurs after triggering a fresh sync cycle on the affected file/folder.
  • Alternative fix: If the error persists, unlink your account from OneDrive Settings → Account → “Unlink this PC,” then sign back in — this forces a complete re-download of all placeholder metadata from the cloud, bypassing local corruption entirely.