Microsoft Teams — Error Code CAA20003 — What It Means & How to Fix It

What Does This Error Mean?

Error CAA20003 is a Teams authentication error — it means Teams tried to verify your identity but something went wrong during the sign-in process. It is often caused by a problem with your system clock, a corporate security policy, or a corrupted authentication token. Your account is not locked or deleted — Teams just cannot complete the login handshake.

Affected Models

Microsoft Teams Desktop App (Windows)
Microsoft Teams Desktop App (Mac)

Common Causes

Your computer's date and time are incorrect, which breaks the authentication process
A corporate conditional access policy is blocking Teams from signing in from your device or network
The authentication token stored on your device is expired or corrupted
A proxy server or VPN is interfering with Teams' connection to Microsoft's login servers
Your Microsoft account password was recently changed and Teams still has the old one cached

How to Fix It

Check your computer's date and time. Right-click the clock in your taskbar, click Adjust date/time, and make sure Set time automatically is turned on. Sync the time if it is off.

Microsoft's authentication system uses time-based tokens. If your clock is more than a few minutes off, authentication fails with this error.
Sign out of Teams, then clear the credentials stored on your PC. Open Windows Credential Manager (search for it in the Start menu), go to Windows Credentials, and delete any entries that mention Microsoft, Teams, or MicrosoftOffice.

Old, stale credentials sitting in Credential Manager can block new sign-in attempts. Deleting them forces Teams to ask for fresh credentials.
Clear the Teams cache. Close Teams fully, then open File Explorer and go to %appdata%\Microsoft\Teams. Delete the contents of the Cache, blob_storage, and Local Storage folders.

A corrupted token stored in the cache is a common cause of CAA20003. Clearing the cache forces Teams to request a fresh token.
If you are using a VPN, disconnect from it and try signing into Teams again. Some VPNs interfere with Microsoft's authentication servers.

If Teams signs in successfully without the VPN, ask your IT team to add Teams to the VPN split-tunneling list so Teams traffic bypasses the VPN.
Try signing into Teams through a web browser at teams.microsoft.com. If the web version works, the issue is specific to the desktop app. Uninstall and reinstall the desktop Teams app.

The web version uses a different authentication flow. If it works, it confirms your account is fine and the desktop app is the problem.

When to Call a Professional

If this error appears on a work laptop and you cannot resolve it yourself, contact your IT department. Conditional access policies are managed by your organization's IT admin and cannot be changed by individual users. Your IT team can also check if your device meets the compliance requirements set by your company.

Frequently Asked Questions

What does CAA20003 actually stand for?

CAA stands for Client Application Authentication. The number 20003 is a specific error code within Microsoft's authentication system. It broadly means the authentication request was denied or could not be completed. Microsoft's documentation classifies it as an authorization failure, meaning Teams received a response from the login server but was not granted access.

My work computer shows CAA20003 but my personal laptop does not. Why?

Your company's IT department likely has conditional access policies that restrict sign-ins to approved devices or networks. If your work computer is not meeting those conditions — for example, it needs a security update or a compliance check — Teams blocks the sign-in and shows CAA20003. Contact your IT department to check if your device is compliant.

I changed my Microsoft password yesterday and now Teams shows this error. Is that why?

Almost certainly yes. When you change your password, Teams may still have your old password cached. Sign out of Teams, clear the Windows Credential Manager entries for Microsoft, and sign back in with your new password. The error should disappear immediately.