How to Fix Teams Error teams-error-caa5004b — Sign In Error [2026]

Teams Error teams-error-caa5004b: Sign In Error

This error typically occurs when corrupted microsoft teams local cache preventing authentication. Below you'll find 5 proven fixes to resolve it.

What Causes Teams Error teams-error-caa5004b?

Teams error teams-error-caa5004b (Sign In Error) can be triggered by several issues:

Corrupted Microsoft Teams local cache preventing authentication
Microsoft account sync issue between Teams and Windows credentials
Corporate proxy blocking Teams authentication endpoints
Outdated Teams app version with known authentication bugs
Multiple Microsoft accounts causing credential conflicts

How to Fix Teams Error teams-error-caa5004b — Step by Step

Clear Teams cache

Close Teams completely (right-click system tray icon > Quit). Press Win + R > type %appdata%\Microsoft\Teams > delete the following folders: Cache, Blob_storage, databases, GPUCache, Local Storage, tmp. Restart Teams and sign in.

Sign out of all Microsoft apps

Sign out from Teams, Outlook, Office, OneDrive, and Windows itself (if using a Microsoft account). Restart. Sign back into Windows first, then Teams. Credential conflicts between apps cause caa5004b.

Disable proxy settings

Settings > Network > Proxy > turn off Automatically detect settings and Use a proxy server. Teams authentication fails through many proxies. On corporate networks, ask IT if Teams is whitelisted through the proxy.

Reinstall Microsoft Teams

Settings > Apps > Microsoft Teams > Uninstall. Also delete C:\Users\[username]\AppData\Local\Microsoft\Teams. Download the latest Teams installer from teams.microsoft.com and reinstall.

Use Teams Web App

Go to teams.microsoft.com in a browser and sign in there while you troubleshoot the desktop app. Teams Web uses the browser's authentication which is separate from the desktop app's credential store.

Still Getting Error teams-error-caa5004b?

IT Cares can diagnose and fix this error remotely — usually in under 30 minutes.

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Frequently Asked Questions

What is Teams error caa5004b?

An authentication error meaning Teams cannot verify your Microsoft account credentials. It may be a corrupted token cache, a credential conflict, or a network issue blocking Microsoft's authentication servers.

Will clearing the Teams cache delete my messages?

No. Teams messages are stored on Microsoft's servers. Clearing the local cache only removes temporary files — your chats, files, and meetings remain intact and re-download when you sign in.

Can a proxy cause caa5004b?

Yes. Teams authenticates through login.microsoftonline.com. If your proxy blocks or modifies traffic to this domain, authentication fails. Corporate IT needs to whitelist Microsoft's authentication endpoints.

Why does the error happen after a password change?

After changing your Microsoft password, Teams may still try to use the old cached credentials. Signing out of all Microsoft apps and signing back in clears the old token.

How do I check if Teams servers are down?

Visit admin.microsoft.com/servicestatus or status.office365.com. Microsoft also posts status updates at Twitter/X @MSFT365Status.

How to Fix Teams Error teams-error-caa5004b — Sign In Error