In addition to being thrown by the account lockout threshold policy, this is a Windows error that typically occurs when a password is repeatedly entered incorrectly, when there are expired passwords, or if there are incorrect DNS settings.
In your case it sounds like there could be a device or service using old credentials that keeps using the old password and trying to log in. You should be able to verify this by checking the event log on the server.
In addition, you can try these steps to resolve the error:
- Follow the steps to unlock the user account and confirm if there are any policies that could be locking out the account: https://docs.microsoft.com/en-us/azure/active-directory-domain-services/troubleshoot-sign-in.
- Create a new user account and use it to log in to the domain.
- Check the DNS settings as described here.
I've moved this post to the Windows section of Q&A, but let me know if you still run into the issue after trying these steps.
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