File Cannot Open

How to Fix Unsupported Authentication Protocol Error in Word and Excel

Emma Brown Oct 8, 2026 869 views

Question details

Users encounter an unsupported authentication protocol error when trying to open files from OneDrive or SharePoint.

How to Fix Unsupported Authentication Protocol Error in Word and Excel

Product: Microsoft Word and Excel
Device & OS: Windows
Scenario: Opening cloud-stored files from OneDrive or SharePoint using desktop Office applications.
Observed behavior: An error message appears stating the server uses an unsupported authentication protocol, preventing the file from opening. Occasionally, the Teams Outlook add-in may also disappear.

Before you start

Ensure you know your correct work or school account credentials and save any locally open documents before signing out of your accounts.

Solution 1Recommended

Clear Cached Credentials and Re-sign Into Office

Removing old or conflicting cached credentials in Windows is the most effective way to resolve authentication protocol errors.

Conflicting personal and work accounts can confuse Office when connecting to SharePoint or OneDrive. Clearing the Windows Credential Manager forces a fresh authentication token.

Sign out of all Office accounts

Open Word or Excel, navigate to File > Account (or click your profile picture at the top right), and select Sign Out for all connected accounts. Close all Office applications.

Open Windows Credential Manager

Press the Windows key, type 'Credential Manager' into the search bar, and hit Enter to open the Control Panel applet.

Remove Office credentials

Select 'Windows Credentials'. Scroll down to the Generic Credentials section, find any entries starting with 'MicrosoftOffice', click on them, and select 'Remove'.

Restart and sign in

Restart your computer. Open Word or Excel and sign in again using your correct work or school account to test opening the OneDrive or SharePoint file.

Clear Cached Credentials and Re-sign Into Office

Tip: Test opening the files directly from the OneDrive synchronized folder in your File Explorer to verify if the connection is restored.

Solution 2

Update Microsoft 365 and Windows

Outdated software builds can cause compatibility issues with modern cloud authentication protocols.

Solution 3

Reset Microsoft 365 Activation State

If clearing credentials fails, resetting the activation state forces Office to re-authenticate completely.

Free Microsoft Office alternative

Switch to WPS Office for a Hassle-Free Document Experience

Tired of dealing with complex Microsoft 365 authentication errors and login loops? WPS Office is a free, lightweight, and highly compatible alternative that lets you open, edit, and save your documents seamlessly.

1. Download WPS Office: Visit the official WPS website and click the free download button.
2. Install the software: Run the downloaded installer and follow the simple on-screen instructions.
3. Open your files: Launch WPS Office and open your existing Word or Excel files instantly.

Free and lightweight alternative to Microsoft OfficeFully compatible with Microsoft Word, Excel, and PowerPoint formatsNo complex cloud authentication required for editing local filesFamiliar user interface allows for a seamless transition without a learning curve

microsoft office alternative - wps office

Frequently Asked Questions

What causes the unsupported authentication protocol error?

This error is typically caused by conflicting personal and work accounts logged in simultaneously, outdated Office software builds, or corrupted cached credentials in your Windows system.

Does this authentication error affect my local files?

Generally, no. This error specifically targets files opened directly from cloud servers like OneDrive or SharePoint. Local files saved on your computer's hard drive should continue to open normally.

Why did my Teams invitation button disappear in Outlook?

The Teams invitation button is provided by the Teams Outlook add-in, which can sometimes disable itself during authentication errors or updates. You can restore it by going to File > Options > Add-ins in Outlook, managing COM Add-ins, and re-checking the Microsoft Teams Meeting Add-in.

Document & File Issues