Microsoft 365 Error Codes

How to Fix Office 365 Sign-In Errors 1200, CAA50021 and CAA80000

Rana Garcia Oct 8, 2026 868 views

Question details

The user cannot sign into Microsoft 365 desktop applications and receives specific error codes, even though logging into the web versions works perfectly.

Fix Office 365 Sign-In Errors 1200, CAA50021, CAA80000, and OneDrive 2603

Product: Microsoft 365, Outlook, Teams, OneDrive
Device & OS: not provided
Scenario: Attempting to authenticate and sign into installed Microsoft desktop applications after standard troubleshooting steps like reinstalling and clearing caches failed.
Observed behavior: Sign-in fails with error codes 1200, CAA50021, CAA80000, and OneDrive error 2603 on desktop apps, while browser-based sign-in functions normally.

Before you start

Ensure you have administrative privileges on your computer, as modifying internet security protocols and resetting system activation states require elevated permissions.

Solution 1Recommended

Enable TLS 1.1 and TLS 1.2 in Internet Options

Activating the correct Transport Layer Security (TLS) protocols ensures secure communication between your computer and Microsoft's authentication servers.

Microsoft 365 desktop apps rely on specific local network configurations to verify your credentials. If TLS 1.1 and TLS 1.2 are disabled on your machine, the apps will fail to connect securely, resulting in sign-in errors like CAA80000.

Open Internet Options

Click the Windows Start menu, type 'Internet Options' into the search bar, and press Enter to launch the Internet Properties window.

Navigate to the Advanced Tab

Click on the 'Advanced' tab located at the top right of the Internet Properties window.

Enable TLS Settings

Scroll down the Settings list to the 'Security' section. Check the boxes next to 'Use TLS 1.1' and 'Use TLS 1.2'.

Apply and Restart

Click 'Apply' and then 'OK' to save your changes. Restart your computer and attempt to sign into your Office applications again.

Enable TLS 1.1 and TLS 1.2 in Internet Options

Check TLS 1.3: If you are on a newer version of Windows, you can also check 'Use TLS 1.3' if it is available in the list to ensure maximum compatibility.

Solution 2

Reset the Microsoft 365 Activation State

Clearing corrupted local activation data forces Office apps to fetch fresh authentication tokens.

Solution 3

Open a Support Ticket via Microsoft 365 Admin

If local network and activation fixes fail, server-side diagnostics are required to find the root cause.

Free Microsoft Office alternative

Switch to WPS Office to Avoid Sign-In Hassles

If persistent Microsoft 365 sign-in errors are disrupting your workflow, consider switching to WPS Office. It provides a lightweight, free alternative that lets you edit your documents locally without relying on complicated cloud activations.

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 quick setup instructions.
3. Open Your Files Seamlessly: Launch WPS Office and directly open your existing Microsoft Office files without worrying about sign-in errors.

Fully compatible with Microsoft Word, Excel, and PowerPoint file formats (.docx, .xlsx, .pptx).No mandatory cloud sign-ins required to create or edit local documents.Lightweight installation with a familiar, easy-to-navigate user interface.Built-in PDF editing tools available right out of the box.

Frequently Asked Questions

Why can I sign into Office 365 on the web but not on desktop applications?

Desktop applications rely on local system settings, such as TLS network protocols and saved credential tokens. If these local caches are corrupted or the required protocols are disabled in Windows, desktop sign-in will fail even if your account is perfectly fine on the web.

What does error code CAA50021 mean?

Error CAA50021 usually means that your device's registration has failed or the authentication token has expired. Disconnecting your account from 'Access work or school' in Windows settings and signing back in generally resolves this issue.

Will reinstalling Microsoft Office fix the 1200 sign-in error?

No, reinstalling Office typically does not fix error 1200. This error is tied to cached credentials, disabled TLS settings, or the system's activation state rather than missing or corrupted application files.

Microsoft Office Error Codes