Microsoft 365 Error Codes

How to Fix Office Unsupported Server Authentication Protocol Errors

John Wilson Oct 1, 2026 869 views

Question details

Users need to resolve an authentication protocol error that appears in Office applications, typically following a OneDrive synchronization.

How to Fix Office Unsupported Server Authentication Protocol Errors

Product: Microsoft Office 365, OneDrive
Device & OS: Windows
Scenario: Synchronizing files with OneDrive or signing into Microsoft 365 applications.
Observed behavior: Microsoft Office displays an unsupported server authentication protocol error message, usually caused by corrupted cached credentials or identity data.

Before you start

Ensure you have saved all your work and completely closed all Microsoft Office applications and the OneDrive client before attempting to clear system caches or modify the registry.

Solution 1Recommended

Clear OneAuth and IdentityCache Folders

This is the most common and effective method to resolve authentication errors by removing corrupted login caches.

Microsoft Office stores temporary identity and authentication data locally. When these files become corrupted or outdated, they can trigger server protocol errors. Deleting them forces Office to generate fresh, error-free credentials.

Open the Run Dialog

Press the Windows key + R on your keyboard to open the Run command window.

Navigate to the Microsoft AppData Folder

Type %localappdata%\Microsoft into the Run dialog box and press Enter.

Delete Cached Folders

Locate the folders named 'OneAuth' and 'IdentityCache'. Right-click each folder and select Delete.

Restart Office

Reopen your Microsoft Office applications and sign in again to verify if the synchronization error is resolved.

Solution 2

Remove the Office Identity Registry Key

If clearing the cache folders does not work, clearing the identity registry keys will remove deeply rooted conflicting account data.

Solution 3

Reset OneDrive and Repair Office

Use this method if the error persists and is heavily tied to OneDrive synchronization failures or a corrupted Office installation.

Free Microsoft Office alternative

Switch to WPS Office for a Hassle-Free Experience

Tired of dealing with complex authentication errors and corrupted caches? WPS Office is a lightweight, free alternative that offers a smooth user experience without complicated server synchronization issues.

1. Download the Installer: Visit the official WPS Office website and download the free version for Windows.
2. Install WPS Office: Run the setup file and follow the quick installation prompts.
3. Open Your Documents: Launch WPS Office and instantly open your existing Microsoft Office files without worrying about formatting issues.

Avoid complex server authentication protocol errorsFully compatible with Microsoft Word, Excel, and PowerPoint file formatsLightweight installation that consumes fewer system resourcesFamiliar user interface for seamless and instant migration

microsoft office alternative - wps office

Frequently Asked Questions

What causes the unsupported server authentication protocol error in Office?

This error is typically caused by corrupted Microsoft 365 cached credentials, outdated identity data in the Windows Registry, or conflicts occurring during OneDrive file synchronization.

Will deleting the IdentityCache and OneAuth folders delete my personal files?

No. These folders only store temporary login and authentication data used by Microsoft services. Deleting them will simply require you to sign back into your Office apps, and your personal documents will remain completely safe.

What should I do if the error persists after trying these fixes?

If the issue continues, you should check for Windows updates, ensure you are running the latest version of Office via the Click-to-Run client, or use the official Microsoft Support and Recovery Assistant (SaRA) tool to diagnose the problem.

Microsoft Office Error Codes