How to Fix Microsoft Teams Error caa2000b

If you encounter Error Code caa2000b while trying to sign in to Microsoft Teams, you are experiencing an authentication request failure. This error is common in hybrid configurations where user identity authentication is federated to an on-premises server (like Active Directory Federation Services or AD FS).

This guide walks you through diagnosing WS-Trust federation issues, clearing cached tokens, and restoring the desktop client connection.

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1. Identify the Exact Meaning of the Error Code

Error Code caa2000b indicates that Microsoft Entra ID was unable to retrieve a valid SAML token from the federated identity provider (IdP).

Common causes include:

• Disabled WS-Trust Endpoints: The AD FS server has disabled or blocked WS-Trust endpoints (specifically /adfs/services/trust/13/windowstransport), which are required for desktop client silent authentication.
• Intranet vs. Extranet Policies: The federation policy restricts desktop authentication when the user is connecting from outside the corporate network.
• AD FS Service Outage: The on-premises federation server is down or returning a configuration error to Entra ID.

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2. Clear Cache or Credentials Related to the Software

Purging local caches forces the system to run a clean AD FS metadata query instead of relying on stale endpoints.

A. Windows PowerShell Commands

1. Terminate all Teams processes:

   Stop-Process -Name "ms-teams" -Force -ErrorAction SilentlyContinue

2. Delete cached folders:

   Remove-Item -Path "$env:LOCALAPPDATA\Packages\MSTeams_8wekyb3d8bbwe\*" -Recurse -Force -ErrorAction SilentlyContinue

3. Remove credentials matching your work account in Windows Credentials Manager.

B. macOS Terminal Commands

1. Close Teams completely.
2. Purge the app data in Terminal:

   pkill -9 "Microsoft Teams"
   rm -rf ~/Library/Group\ Containers/UBF8T346G9.com.microsoft.teams
   rm -rf ~/Library/Containers/com.microsoft.teams2

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3. Check Service Server Status for Outages

Because caa2000b points to local AD FS configurations, checking server uptime is critical.

• Ping your organization’s AD FS login URL (e.g., sso.yourcompany.com) to verify it is responsive.
• Check the Microsoft 365 Service Status Page to confirm Entra ID is operating normally.
• Contact your IT department to confirm whether the AD FS services are undergoing maintenance.

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4. Perform a Repair or Reset on the Desktop Client

Resetting the application forces the underlying WAM authentication framework to update its AD FS configuration endpoints.

A. Reset Teams on Windows

1. Execute this PowerShell command as Administrator:

   Get-AppxPackage -Name "MSTeams" -AllUsers | Reset-AppxPackage

B. Update Root Certificates (Windows)

If your federation server uses an internal Certificate Authority, ensure your client trust store is updated:

1. Run PowerShell as Administrator.
2. Force a root certificate update:

   Certutil -generateSSTFromWU RootCerts.sst

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5. Re-authenticate the Connection to Sync Files

Bypassing federated desktop endpoints can help restore access.

A. Reconnect Work/School Account

1. Open Settings → Accounts → Access work or school.
2. Select your account, click Disconnect, and confirm.
3. Reboot.
4. Click Connect and sign in again. This forces Windows to query the AD FS endpoints from scratch.

B. Authenticate via Modern Auth Web Client

1. Open a browser in private mode.
2. Go to https://teams.microsoft.com.
3. If this succeeds, your credentials and the AD FS server are working, but the client WS-Trust protocol is blocked. Inform your IT department to ensure the /adfs/services/trust/13/windowstransport endpoint is enabled.

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6. Summary Quick Reference Checklist

Action	Practical Resolution	Expected Outcome
Verify Web Login	Log in to teams.microsoft.com in Private browser	Isolates WS-Trust desktop failure from generic account locks.
Clear App Cache	Purge %localappdata%\Packages\MSTeams_8wekyb3d8bbwe	Eliminates stale token requests.
Re-register Work Connection	Disconnect/Reconnect under Windows settings	Renews domain-join tokens.
Contact Admin for AD FS	Verify ADFS /adfs/services/trust/13/ endpoint is enabled	Fixes the root server-side federation issue.
Reset Desktop Client	Run Reset-AppxPackage	Restores default Teams configuration.