How to Fix Outlook File Not Found or Calendar Sync Failure Errors

Microsoft Outlook can sometimes show errors like “File not found”, “Cannot open this item”, or Calendar sync failed, especially when opening calendar items, sending meeting invites, or syncing with Exchange, Microsoft 365, or IMAP accounts. These errors can block scheduling, meeting updates, and even normal mailbox access.

In most cases, Outlook file not found or calendar sync failure errors are caused by corrupted Outlook data files (OST/PST), profile issues, sync conflicts, add-ins, or connectivity problems, not deleted calendar data. The steps below will help you fix the issue safely and restore normal syncing.

How to Fix Outlook File Not Found or Calendar Sync Failure Errors

Follow the steps in order. After each step, reopen Outlook and check whether the calendar sync issue is resolved.

1. Restart Outlook and Your PC

Temporary sync locks can cause file and calendar errors.

1. Close Microsoft Outlook completely
2. Restart your computer
3. Open Outlook again and let it finish syncing

This clears background sync processes and cached locks.

2. Check Internet and Account Connection

Calendar sync requires a stable connection.

1. Make sure your PC is connected to the internet
2. Disable VPN temporarily
3. Check Outlook status bar:
   • “Connected to Microsoft Exchange”
   • “All folders are up to date”

Offline or unstable connections often trigger calendar errors.

3. Run Outlook in Safe Mode

Add-ins frequently cause calendar and file access errors.

1. Press Windows + R
2. Type:

outlook.exe /safe

3. Press Enter
4. Try opening the calendar

If the error is gone in Safe Mode, an add-in is the cause.

4. Disable Problematic Outlook Add-ins

If Safe Mode works, disable add-ins permanently.

1. Open Outlook normally
2. Go to File > Options > Add-ins
3. At the bottom, select COM Add-ins > Go
4. Uncheck all add-ins
5. Restart Outlook
6. Re-enable add-ins one by one to find the culprit

Calendar sync errors are often add-in related.

5. Check and Repair Outlook Data Files (PST / OST)

Corrupted data files commonly cause “File not found” errors.

For PST files

1. Close Outlook
2. Locate SCANPST.EXE (Inbox Repair Tool)
3. Select your .pst file
4. Click Start and repair errors

For OST files (Exchange / Microsoft 365)

1. Close Outlook
2. Go to:

C:\Users\YourUsername\AppData\Local\Microsoft\Outlook

3. Rename the .ost file
4. Reopen Outlook

Outlook will recreate the OST file automatically.

6. Rebuild the Outlook Calendar Cache

Calendar cache corruption can break syncing.

1. Close Outlook
2. Press Windows + R
3. Run:

outlook.exe /cleanviews

4. Restart Outlook

This resets calendar views and cached metadata.

7. Check Mailbox Size and Sync Conflicts

Large or conflicted calendars may fail to sync.

1. Open Outlook
2. Go to Folder > Properties > Synchronization
3. Check for sync errors or conflicts
4. Resolve or delete duplicate calendar items if found

Sync conflicts often surface as “file not found” errors.

8. Create a New Outlook Profile (Very Effective)

Profile corruption is a top cause of calendar failures.

1. Close Outlook
2. Open Control Panel > Mail > Show Profiles
3. Click Add
4. Create a new profile
5. Set it as Default
6. Open Outlook using the new profile

This fixes most persistent calendar and file errors.

9. Update or Repair Microsoft Office

Outdated or damaged Office files can break Outlook sync.

1. Open Settings > Apps > Installed apps
2. Select Microsoft 365 / Office
3. Click Modify
4. Choose Quick Repair
5. If needed, run Online Repair

Repairing Office often resolves calendar sync issues.

10. Check Server-Side Issues (Exchange / Microsoft 365)

If errors persist across devices:

1. Test Outlook Web (outlook.office.com)
2. Check if calendar works there
3. Review Microsoft 365 service health
4. Contact your IT admin if on a work account

If the calendar fails online, the issue is server-side.

Final Thoughts

Outlook “File not found” and Calendar sync failure errors are almost always caused by data file corruption, add-ins, or profile issues, not missing calendar entries. In most cases, rebuilding the OST file or creating a new Outlook profile fixes the problem completely.

To avoid future sync problems, keep Outlook updated, limit unnecessary add-ins, and allow Outlook to fully sync before closing it.