Microsoft Teams Error CAA20003: 13 Ways to Fix Sign-In

Quick Fix

Microsoft Teams error CAA20003 is a sign-in problem. To fix it: Clear Teams cache – close Teams completely, press Windows+R, type %appdata%\Microsoft\Teams, delete all files inside, then restart Teams. If that doesn’t work, sign out of all Microsoft 365 accounts and sign back in. This fixes CAA20003 for most users.

What Is Microsoft Teams Error CAA20003?

Error CAA20003 occurs when Microsoft Teams cannot authenticate your account. You’ll see a message like “We couldn’t sign you in” or “Something went wrong” followed by the error code. This prevents you from logging into Teams and accessing your chats, meetings, and files.

Common causes include corrupted Teams cache, expired credentials, conflicts with other Microsoft accounts, certificate issues, proxy/firewall blocking authentication, or problems with Azure Active Directory. Let’s fix it step by step.

Method 1: Clear Microsoft Teams Cache

Corrupted cache files are the most common cause of CAA20003.

1. Close Microsoft Teams completely (check system tray)
2. Press Ctrl + Shift + Esc to open Task Manager
3. End any Microsoft Teams processes
4. Press Windows + R
5. Type %appdata%\Microsoft\Teams and press Enter
6. Delete all files and folders inside (Ctrl + A, then Delete)
7. Restart Microsoft Teams
8. Sign in again

Alternative – Clear All Cache Folders:

Delete contents from these folders:

• %appdata%\Microsoft\Teams\Cache
• %appdata%\Microsoft\Teams\blob_storage
• %appdata%\Microsoft\Teams\databases
• %appdata%\Microsoft\Teams\GPUcache
• %appdata%\Microsoft\Teams\IndexedDB
• %appdata%\Microsoft\Teams\Local Storage
• %appdata%\Microsoft\Teams\tmp

Method 2: Clear Windows Credentials

Stored credentials might be corrupted or expired.

1. Press Windows key and type “Credential Manager”
2. Open Credential Manager
3. Click “Windows Credentials”
4. Find all entries related to:
   • Microsoft Teams
   • Microsoft Office
   • MicrosoftAccount
   • Any entries with “teams” or “office”
5. Click each one and select “Remove”
6. Also check “Web Credentials” and remove Microsoft entries
7. Restart your computer
8. Open Teams and sign in fresh

Method 3: Sign Out of All Microsoft Accounts

Account conflicts cause authentication errors.

In Windows Settings:

1. Go to Settings > Accounts > Email & accounts
2. Remove any work/school accounts you don’t need
3. Go to Settings > Accounts > Access work or school
4. Disconnect any connected accounts
5. Restart your computer
6. Open Teams and sign in with only the account you need

In Microsoft 365 Apps:

1. Open any Microsoft 365 app (Word, Excel)
2. Click your profile picture (top right)
3. Click “Sign out” from all accounts
4. Sign back into the correct account
5. Try Teams

Method 4: Reset Teams via Settings

Windows can repair or reset Teams app.

1. Go to Settings > Apps > Installed apps
2. Search for “Microsoft Teams”
3. Click the three dots and select “Advanced options”
4. Scroll down and click “Repair” first
5. Try Teams – if still failing, go back
6. Click “Reset” (this clears all data)
7. Open Teams and sign in

Method 5: Check Date and Time Settings

Incorrect time causes authentication certificate errors.

1. Right-click the clock in the taskbar
2. Select “Adjust date and time”
3. Enable “Set time automatically”
4. Enable “Set time zone automatically”
5. Click “Sync now”
6. Restart Teams

If your organization uses a specific time server, check with IT.

Method 6: Disable Proxy Settings

Proxy configurations can interfere with Teams authentication.

1. Press Windows + I to open Settings
2. Go to Network & internet > Proxy
3. Turn OFF “Automatically detect settings”
4. Turn OFF “Use a proxy server”
5. Restart Teams

If you’re on a corporate network that requires proxy, contact your IT department.

Method 7: Allow Teams Through Firewall

Firewall might be blocking Teams authentication servers.

1. Press Windows key and type “Firewall”
2. Open “Windows Defender Firewall”
3. Click “Allow an app or feature through Windows Defender Firewall”
4. Click “Change settings”
5. Find Microsoft Teams and check both Private and Public
6. Click OK

Corporate Firewalls:

IT may need to whitelist these Microsoft endpoints:

• *.microsoft.com
• *.microsoftonline.com
• *.teams.microsoft.com
• *.skype.com
• login.microsoftonline.com

Method 8: Disable VPN

VPN connections often interfere with Microsoft authentication.

1. Disconnect from any VPN
2. Try signing into Teams
3. If it works, you may need to configure VPN split tunneling
4. Or add Teams to VPN exceptions

Method 9: Update Microsoft Teams

Outdated Teams can have authentication bugs.

If you can open Teams:

1. Click your profile picture
2. Select “Check for updates”
3. Install any available updates
4. Restart Teams

If you can’t open Teams:

1. Uninstall Teams from Settings > Apps
2. Download the latest version from teams.microsoft.com
3. Install and sign in

Method 10: Use Web Version

As a workaround, use Teams in your browser.

1. Open teams.microsoft.com in Chrome, Edge, or Firefox
2. Sign in with your account
3. Click “Use the web app instead”
4. Access your chats and meetings while troubleshooting the desktop app

Method 11: Check Azure AD Status

If you’re in an organization, Azure AD might have issues.

1. Visit status.office.com
2. Check for any Azure Active Directory or Teams outages
3. Ask colleagues if they’re having the same issue
4. Contact your IT department

If it’s a service outage, you’ll need to wait for Microsoft to resolve it.

Method 12: Reinstall Microsoft Teams

A clean reinstall often fixes persistent authentication errors.

1. Close Teams and end all processes in Task Manager
2. Go to Settings > Apps > Installed apps
3. Find Microsoft Teams and click “Uninstall”
4. Press Windows + R, type %appdata%
5. Delete the Microsoft\Teams folder
6. Press Windows + R, type %localappdata%
7. Delete the Microsoft\Teams folder
8. Restart your computer
9. Download Teams from teams.microsoft.com
10. Install and sign in

Method 13: Check TLS Settings

Teams requires TLS 1.2 for secure authentication.

1. Press Windows + R, type inetcpl.cpl, press Enter
2. Go to the Advanced tab
3. Scroll to the Security section
4. Ensure “Use TLS 1.2” is checked
5. You can uncheck TLS 1.0 and TLS 1.1
6. Click OK
7. Restart your computer

For IT Administrators

If multiple users experience CAA20003:

• Check Azure AD Connect synchronization status
• Verify federation services (ADFS) are working
• Check conditional access policies aren’t blocking Teams
• Ensure required URLs and ports are allowed through firewall
• Review any recent changes to authentication policies

FAQ

What does Microsoft Teams error CAA20003 mean?

Error CAA20003 indicates an authentication failure. Teams cannot verify your credentials with Microsoft servers. This is usually caused by corrupted cache, expired credentials, network issues, or problems with Azure Active Directory.

Why do I keep getting CAA20003 after clearing cache?

If clearing cache doesn’t help, try: removing stored credentials from Credential Manager, checking proxy/VPN settings, ensuring date/time is correct, and signing out of all Microsoft accounts before signing back in. Corporate network restrictions can also cause persistent issues.

Does CAA20003 mean my account is locked?

Not necessarily. The error is usually on the client side (your computer), not the account. However, if you’ve entered wrong passwords multiple times, your account may be locked. Contact your IT administrator or try resetting your password at account.microsoft.com.

Can I use Teams while error CAA20003 appears?

The desktop app won’t work, but you can use the web version at teams.microsoft.com. This workaround lets you access chats and meetings while you troubleshoot the desktop app.

Why does CAA20003 only affect one user?

Single-user issues typically indicate local problems: corrupted cache, conflicting accounts, credential issues, or local firewall/security software blocking authentication. Try the troubleshooting steps on that specific computer.

Should I contact IT or Microsoft about CAA20003?

First try the fixes above. If you’re in an organization and multiple people have the issue, contact IT – it could be an Azure AD or network configuration problem. Contact Microsoft support only if you’ve exhausted all troubleshooting steps.