The error typically indicates a problem with authentication or encryption negotiation between Outlook and Azure Active Directory (AAD).
This error is often tied to.
- Corrupted AAD Broker Plugin cache
- Issues with token acquisition or encryption keys
- Outdated Outlook or Windows components
- Firewall or antivirus interference
Please try the solutions below to overcome this issue.
1. Clear AAD Broker Plugin Cache
Navigate to: C:\Users\<YourUsername>\AppData\Local\Packages\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy\AC\TokenBroker\Account
- Delete all files in this folder.
- Reboot your device.
- Try signing in to Outlook again
2. Run Microsoft 365 Sign-In Troubleshooter
- Download and run the Microsoft Support and Recovery Assistant (SaRA) tool.
- Choose Outlook > I can't sign in and follow the prompts.
3. Update Outlook and Windows
- Open Outlook → File > Office Account > Update Options > Update Now
- Ensure Windows is fully updated via Settings > Windows Update
4. Rebuild Outlook Profile
- Go to Control Panel > Mail > Show Profiles
- Create a new profile and set it as the default.
- Re-add your account.
Note. One of these methods will fix your issue.
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