What causes AADSTS81009?

Kerberos ticket for the AZUREADSSOACC computer account is encrypted with an outdated password (decryption key rotated but not re-synced to on-prem AD). Client falls back to NTLM instead of Kerberos because the Azure AD URLs (autologon.microsoftazuread-sso.com) are not in the browser's Intranet/Trusted Sites zone. Multiple AZUREADSSOACC accounts exist in on-prem AD after a forest re-onboarding, causing ticket/key mismatches. Time skew >5 minutes between the client, the on-prem domain controller, and Azure AD. User signs in from a non-domain-joined device or over a network where Kerberos to the on-prem KDC is unreachable (no line-of-sight to a DC)

How do I fix AADSTS81009?

Roll the Kerberos decryption key of the AZUREADSSOACC$ computer account: on the Azure AD Connect server run `Update-AzureADSSOForest` from the `AzureADSSO.psm1` module — this resyncs the password between on-prem AD and Azure AD / Entra ID. Verify only ONE AZUREADSSOACC computer object exists per forest (`Get-ADComputer -Filter "Name -eq 'AZUREADSSOACC'"`); delete duplicates left over from previous Seamless SSO enablements. Push the Intranet Zone policy via GPO so `https://autologon.microsoftazuread-sso.com` is in the Local Intranet zone and 'Automatic logon only in Intranet zone' is enabled — without this the browser sends NTLM and the header is rejected. Confirm time sync: client, DC, and Azure AD Connect server must be within 5 minutes (`w32tm /query /status`). Reproduce with Fiddler/network trace and inspect the `Authorization: Negotiate` header — if it starts with `TlRMTVNT` (NTLM) instead of `YII` (Kerberos), the issue is client-side zone configuration, not the AZUREADSSOACC key

Low severityauthentication

Power BI Error:
AADSTS81009

What does this error mean?

Azure AD / Entra ID rejects the Kerberos ticket sent by Seamless SSO because the Authorization header is malformed or the ticket is invalid.

Common causes

1Kerberos ticket for the AZUREADSSOACC computer account is encrypted with an outdated password (decryption key rotated but not re-synced to on-prem AD)
2Client falls back to NTLM instead of Kerberos because the Azure AD URLs (autologon.microsoftazuread-sso.com) are not in the browser's Intranet/Trusted Sites zone
3Multiple AZUREADSSOACC accounts exist in on-prem AD after a forest re-onboarding, causing ticket/key mismatches
4Time skew >5 minutes between the client, the on-prem domain controller, and Azure AD
5User signs in from a non-domain-joined device or over a network where Kerberos to the on-prem KDC is unreachable (no line-of-sight to a DC)

How to fix it

1Roll the Kerberos decryption key of the AZUREADSSOACC$ computer account: on the Azure AD Connect server run `Update-AzureADSSOForest` from the `AzureADSSO.psm1` module — this resyncs the password between on-prem AD and Azure AD / Entra ID
2Verify only ONE AZUREADSSOACC computer object exists per forest (`Get-ADComputer -Filter "Name -eq 'AZUREADSSOACC'"`); delete duplicates left over from previous Seamless SSO enablements
3Push the Intranet Zone policy via GPO so `https://autologon.microsoftazuread-sso.com` is in the Local Intranet zone and 'Automatic logon only in Intranet zone' is enabled — without this the browser sends NTLM and the header is rejected
4Confirm time sync: client, DC, and Azure AD Connect server must be within 5 minutes (`w32tm /query /status`)
5Reproduce with Fiddler/network trace and inspect the `Authorization: Negotiate` header — if it starts with `TlRMTVNT` (NTLM) instead of `YII` (Kerberos), the issue is client-side zone configuration, not the AZUREADSSOACC key

Frequently asked questions

What does AADSTS81009 mean?

Unable to validate user's Kerberos ticket.

How do I fix this error?

Check your application registration, token configuration, and user permissions in the Azure portal. Review Conditional Access policies if the error is policy-related.

Source · learn.microsoft.com/en-us/entra/identity-platform/reference-error-codes#aadsts-error-codes