Microsoft 365 Error Codes

Fix Microsoft 365 Sign-In Failed Error 29 in Word and Excel

Maira Mehtab Sep 20, 2026 869 views

Question details

The user is experiencing a recurring authentication failure (Error 29) across Microsoft 365 applications, which constantly prompt for sign-in while still allowing the apps to be used.

Product: Microsoft 365 Apps
Device & OS: not provided
Scenario: Attempting to use Microsoft desktop applications like Word, Excel, and Outlook without continuous sign-in interruptions.
Observed behavior: The applications repeatedly request the user to sign in, then report that the sign-in failed with Error 29, even though web sign-in works and the desktop apps remain functional.

Before you start

Verify your Microsoft 365 subscription status online and ensure you can successfully sign in via a web browser before modifying desktop application files.

Solution 1Recommended

Clear the OneAuth and IdentityCache Folders

Deleting cached identity files forces Microsoft 365 to rebuild your authentication tokens, which often resolves Error 29.

Corrupted local authentication caches are a primary cause of repetitive sign-in loops in Microsoft 365 apps.

Close all applications

Ensure Word, Excel, Outlook, and any other Microsoft 365 applications are completely closed.

Open Local AppData

Press the Windows Key + R to open the Run dialog, type %localappdata%\Microsoft, and press Enter.

Delete OneAuth contents

Locate the OneAuth folder, open it, and delete all the files inside.

Delete IdentityCache contents

Go back to the Microsoft folder, locate the IdentityCache folder, open it, and delete all the files inside.

Restart and sign in

Restart your computer, open a Microsoft 365 application, and sign in again.

Solution 2

Delete the Office Identity Registry Key

Removing corrupted registry identity keys can resolve stubborn sign-in loops that cache clearing does not fix.

Solution 3

Perform a Clean Uninstall and Offline Reinstall

If caching and registry fixes fail, completely removing Office and using an offline installer bypasses corrupted installation files.

Free Microsoft Office alternative

Switch to WPS Office for a Hassle-Free Experience

If Microsoft 365 sign-in errors like Error 29 are disrupting your workflow, consider switching to WPS Office. It provides a lightweight, free, and highly compatible alternative without frustrating subscription authentication loops.

1. Download the installer: Visit the official WPS Office website and click the free download button.
2. Install the software: Run the downloaded executable file and follow the quick installation wizard.
3. Open and edit files: Launch WPS Office to instantly open and edit your existing Microsoft Office documents without sign-in barriers.

Fully compatible with Microsoft Word, Excel, and PowerPoint formatsWork offline without recurring subscription sign-in errorsLightweight application that runs smoothly on most devicesFamiliar user interface for a zero-learning-curve migration

microsoft office alternative - wps office

Frequently Asked Questions

What causes Microsoft 365 Error 29?

Error 29 typically indicates a conflict or corruption within the authentication tokens or identity caching in your Microsoft 365 desktop applications, causing them to repeatedly fail to verify your subscription status.

Why can I still use Word and Excel despite the sign-in failed error?

Microsoft 365 applications have a grace period that allows limited offline functionality when authentication fails. The local license token is temporarily valid, but you must resolve the error before the grace period expires to maintain full access.

Will rolling back Office to an earlier version fix Error 29?

Yes, if Error 29 was triggered by a recent update bug, using the command prompt to roll back Microsoft 365 to a previous build can act as a temporary workaround until Microsoft releases a patch.

Microsoft Office Error Codes