Sign-in & Login Problems

How to Fix Microsoft 365 Desktop App Sign-In and Sync Errors (Error 29)

Steve K Sep 28, 2026 868 views

Question details

The user is experiencing persistent sign-in and synchronization errors on Microsoft 365 desktop applications, despite web versions working properly.

How to Fix Microsoft 365 Desktop App Sign-In and Sync Errors

Product: Microsoft 365 Desktop Apps
Device & OS: Windows
Scenario: Attempting to sign in to Microsoft 365 desktop apps or sync files with OneDrive.
Observed behavior: The applications display expired credentials, deactivated product warnings, or sign-in error 29. Reinstalling Microsoft 365, OneDrive, and Windows does not resolve the issue.

Before you start

Ensure all Microsoft Office applications are completely closed before attempting to clear cache files. It is highly recommended to create a system restore point or back up your registry before making any changes.

Solution 1Recommended

Clear the Microsoft Authentication and Identity Cache

Deleting corrupted authentication cache files forces Microsoft 365 to prompt for fresh credentials, which often resolves persistent sign-in issues.

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\ and press Enter to open the local application data folder for Microsoft.

Locate and back up cache folders

Find the folders named 'OneAuth' and 'IdentityCache'. Copy these folders to your Desktop as a temporary backup.

Delete the cache folders

After backing them up, delete the 'OneAuth' and 'IdentityCache' folders from the Microsoft directory.

Restart and sign in

Restart your computer, open a Microsoft 365 application like Word, and try signing in again.

Clear the Microsoft Authentication and Identity Cache

Quick Fix: For many users, simply clearing the OneAuth and IdentityCache folders is enough to temporarily or permanently fix Error 29.

Solution 2

Reset Office Identity via Registry Editor

If clearing the cache does not work, resetting the Office Identity registry key can clear deep-seated credential conflicts causing the deactivated product error.

Solution 3

Reinstall Microsoft 365 Using an Offline Installer

Bypassing the standard web installer can sometimes circumvent connectivity and sync bugs that trigger persistent sign-in errors.

Free Microsoft Office alternative

Switch to WPS Office for a Hassle-Free Offline Experience

If Microsoft 365 continues to experience sign-in blocks, expired credentials, and synchronization errors, consider switching to WPS Office. It provides a lightweight, highly compatible, and free alternative that lets you work locally without constantly forcing cloud authentication.

1. Download WPS Office: Visit the official WPS website to download the free, lightweight installer.
2. Open Your Existing Files: Launch WPS Office and directly open your Microsoft Word, Excel, or PowerPoint files without losing any formatting.
3. Work Without Interruptions: Enjoy a stable editing environment where local saves and offline work are never blocked by cloud sign-in errors.

Fully compatible with Microsoft Office formats (.docx, .xlsx, .pptx).Work offline seamlessly without forced sign-in interruptions or error 29.Lightweight installation with blazing fast launch speeds.Familiar user interface requiring zero learning curve for Office users.

microsoft office alternative - wps office

Frequently Asked Questions

What is Microsoft 365 Error 29?

Error 29 is a Microsoft 365 activation and sign-in error that typically occurs when the local identity cache becomes corrupted or conflicts with the server's authentication token.

Why do Microsoft apps say my product is deactivated when I have an active subscription?

This happens when the desktop application cannot synchronize with Microsoft's servers due to a corrupted local cache, network issues, or outdated registry keys, causing it to fall back to an unverified or deactivated state.

Can I use Microsoft Office apps without signing in?

No, Microsoft 365 desktop apps require periodic sign-ins to verify your subscription status. If you prefer working offline without mandatory sign-ins, consider using a free alternative like WPS Office.

How do I safely back up my Windows Registry before making changes?

Open the Registry Editor, right-click the specific key or folder you plan to modify, select 'Export', choose a safe location (like your Desktop), and save the .reg file.

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