Most likely causes:

• The username supplied to IIS is invalid.
• The password supplied to IIS was not typed correctly.
• Incorrect credentials were cached by the browser.
• IIS could not verify the identity of the username and password provided.
• The resource is configured for Anonymous authentication, but the configured anonymous account either has an invalid password or was disabled.
• The server is configured to deny login privileges to the authenticating user or the group in which the user is a member.
• Invalid Kerberos configuration may be the cause if all of the following are true:
• Integrated authentication was used.
• the application pool identity is a custom account.
• the server is a member of a domain.

Things you can try:

• Verify that the username and password are correct, and are not cached by the browser.
• Use a different username and password.
• If you are using a custom anonymous account, verify that the password has not expired.
• Verify that the authenticating user or the user's group, has not been denied login access to the server.
• Verify that the account was not locked out due to numerous failed login attempts.
• If you are using authentication and the server is a member of a domain, verify that you have configured the application pool identity using the utility SETSPN.exe, or changed the configuration so that NTLM is the favored authentication type.
• Create a tracing rule to track failed requests for this HTTP status code. For more information about creating a tracing rule for failed requests, click here.

Detailed Error Information:

More Information:

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Microsoft Knowledge Base Articles:

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