The credential is invalid. Unexpected sub status (6008).

Question

The credential is invalid. Unexpected sub status (6008).

Tyler Cox 20

Screenshot (37)

I have been struggling for a while to figure out how to overcome this issue in Outlook (classic). It's only an issue on one of my computers. The app works fine on my other computer and my phones. Can someone help me?

Thank you.

Hornblower409 14,915 Reputation points

2026-08-14T15:28:46.5133333+00:00

@Tyler Cox

Based on your screen shot, you are using New Outlook for Windows. Not Classic Outlook. You might want to edit your question and update your tags.
https://learn.microsoft.com/en-us/answers/support/edit

This looks to be a custom domain work account. Have you tried removing an re-adding the account?
https://support.microsoft.com/en-us/outlook/getstarted/add-an-email-account-to-outlook-for-windows

Answer accepted by question author

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Your answer

Hornblower409 14,915 Reputation points

2026-08-14T15:28:46.5133333+00:00

@Tyler Cox

Based on your screen shot, you are using New Outlook for Windows. Not Classic Outlook. You might want to edit your question and update your tags.
https://learn.microsoft.com/en-us/answers/support/edit

This looks to be a custom domain work account. Have you tried removing an re-adding the account?
https://support.microsoft.com/en-us/outlook/getstarted/add-an-email-account-to-outlook-for-windows

Answer 1

Since the problem happens on only one PC, the most likely cause is stale local sign-in data or a broken device/account registration on that machine.

Try these steps in order:

Close Outlook and sign out of Microsoft apps
- Sign out of Outlook and other Office apps on that PC.
- Close all Office apps.
Disconnect and reconnect the account in Windows
- Open Settings > Accounts > Access work or school.
- If the account appears there, select it and choose Disconnect.
- Then choose Connect and sign in again.
- Restart the PC after reconnecting.
Clear saved credentials
- Open Control Panel > User Accounts > Credential Manager.
- Check both Windows Credentials and Generic Credentials.
- Remove entries related to Microsoft 365, Office, Outlook, or the affected account.
Clear the AAD Broker cache
- In File Explorer, open: %localappdata%\Packages\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy
- Delete the files and folders inside.
- If Windows says files are in use, sign out of Windows or close related Office/Edge processes first.
Restart the PC and add the account again in Outlook
- After restart, open Outlook and sign in again.

If Outlook still keeps prompting for credentials, also check the Outlook profile setting below:

Verify Outlook authentication setting
- In the Outlook profile settings for the Exchange account, open the Security tab.
- Make sure Logon network security is set to Anonymous Authentication.
- A different value can cause repeated credential prompts.

If the account is a work or school account and the issue started after hardware changes or a crash, the local device registration or cached credentials may be out of sync. In that case, the documented next step is to have the Microsoft 365 admin open a support request through the Microsoft 365 Admin Center > Support > Help & Support.