Access-related error when logging into Microsoft Teams

Question

I keep getting an "Access denied" error when logging into MICROSOFT TEAMS.

I have attached the error details below; please review the permissions.

Error Details

Session ID: [Moderator note: Personally Identifiable Information removed]

Error Code: 401

Answer 1

Dear @NIPPON PAINT MARINE KOREA CO.,LTD,

An Error Code 401 (Unauthorized) indicates an authentication failure or a missing permission level required to access Microsoft Teams. This usually occurs for one of three reasons:

1. Missing or Unassigned License: Your account does not currently have an active Microsoft Teams license assigned by your tenant administrator.
2. Stale Authentication Tokens: Corrupted or expired cached credentials in your Teams app are failing to authenticate with Entra ID (formerly Azure AD).
3. Conditional Access Policies: Your organization’s IT policies (such as device compliance or location-based access) are blocking your session.

The following steps are suggested to address the problem:

1. Test on Teams Web App (Quick Verification):
   • Open an InPrivate / Incognito browser window and sign in to teams.microsoft.com.
   • If you can log in via the web, the issue is local cache on your app.
   • If you cannot log in on the web, the issue is account or license-related.
2. Clear the Teams Desktop App Cache (If Web Works):
   • Close Microsoft Teams completely.
   • Press Win + R, paste %appdata%\Microsoft\Teams (or %localappdata%\Packages\MSTeams_8wekyb3d8bbwe for New Teams), and delete all files inside the folder.
   • Restart Teams and attempt to log in again.
   Please refer to this document: Clear the Teams client cache
3. Contact Your M365 / IT Administrator (If Web Fails):
   • Request your IT team to verify in the Microsoft 365 Admin Center that an active Teams license is assigned under Users > Active users > Your Name > Licenses and apps.
   • Ask them to review Entra ID sign-in logs using your Session ID to check if any Conditional Access policy blocked your sign-in attempt.

Please try logging in via the web first and let me know the result so I can guide you further if needed.

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