How to Fix Microsoft 365 Error CAA50021
When trying to sign in to Microsoft 365 apps like Teams, Outlook, or OneDrive, you might see this error:
Something went wrong. We couldn’t sign you in. Error code: CAA50021.
It usually means your device couldn’t connect or register properly with Azure Active Directory (Azure AD). Let’s break down why it happens and how you can fix it.
Why Does Error CAA50021 Happen?
This error can show up for several reasons:
- Your device isn’t properly registered in Azure AD.
- Mobile Device Management (Intune or Microsoft 365 MDM) isn’t enabled.
- Cache files for apps like Teams have become corrupted.
- Your work or school account got unlinked.
- Security software or antivirus is blocking the sign-in process.
- Outdated Microsoft 365 apps.
Quick Things to Try First
Before diving into advanced fixes:
- Restart your computer.
- Make sure you’re not connected to a VPN.
- Check your internet connection.
If the problem continues, move on to the solutions below.
Step-by-Step Fixes
1. Re-register Your Device in Azure AD
This often solves the problem when the registration has expired.
- Press Win + R, type cmd, and press Enter.
- In Command Prompt, type:
dsregcmd /leave
and press Enter. - Open Certificate Manager (press Win + R, type
certmgr.msc).- Delete certificates named MS-Organization-Access and MS-Organization-P2P-Access.
- In Command Prompt, type:
dsregcmd /status
Make sure AzureAdJoined shows NO. - Open Task Scheduler → Microsoft → Windows → Workplace Join.
- Enable and run Automatic-Device-Join.
- Restart your computer.
2. Check Azure AD Settings (Admin Needed)
If you’re not an admin, contact your IT team.
- Go to the Azure AD Admin Center.
- Navigate to Devices → Device Settings.
- Make sure users are allowed to register their devices with Azure AD.
3. Repair or Reset Microsoft 365 Apps
If app files are corrupted, repairing can help.
- Press Win + R, type appwiz.cpl, and press Enter.
- Select Microsoft Office → Change → Repair.
- If repair doesn’t work, try a full Reset or reinstall.
4. Update Microsoft 365 and Teams
- Open any Office app (like Word).
- Go to File → Account → Update Options → Update Now.
- For Teams, download and install the latest version.
5. Clear Microsoft Teams Cache
- Close Teams completely.
- Press Win + R, type:
%appdata%\Microsoft\Teams - Delete all files in that folder.
- Restart Teams and sign in again.
6. Check Antivirus or Security Software
Sometimes antivirus tools block logins. Try disabling it temporarily, then test the sign-in. If it works, add Microsoft 365 apps to the antivirus allow-list.
When to Contact Support
If none of the above fixes work, the issue might be on your organization’s side. Contact your system administrator or Microsoft Support. Share the error code and timestamp so they can trace the problem faster.
Summary: Error CAA50021 is usually tied to Azure AD device registration or corrupted app data. Re-registering your device, repairing apps, clearing cache, and updating software are the main fixes. If it still doesn’t resolve, your IT admin will need to step in.
