Low severityauthentication
Power BI Error:
AADSTS90091, Microsoft Graph unreachable during sign-in
What does this error mean?
Microsoft Entra ID (Azure AD) could not reach Microsoft Graph while resolving the user or tenant during authentication.
Common causes
- 1Transient unavailability of the Microsoft Graph service during the sign-in token issuance
- 2Active Microsoft 365 / Entra ID service incident (check the Microsoft 365 Service Health dashboard)
- 3Conditional Access policy evaluation that requires a Graph call (e.g. group-based assignment) failing because Graph is slow or unreachable
- 4Throttling against Microsoft Graph from the tenant when many sign-ins resolve group/role membership simultaneously
- 5Network egress / firewall issue blocking graph.microsoft.com from the client or on-prem federation server (ADFS, Entra Connect)
How to fix it
- 1Retry the sign-in or refresh — AADSTS90091 is transient in the majority of cases and clears within seconds to minutes.
- 2Check the Microsoft 365 Service Health dashboard (admin.microsoft.com → Health → Service health) and the Azure status page for an active Microsoft Graph or Entra ID incident before troubleshooting your own configuration.
- 3If the error persists for one user/app only: review Conditional Access policies that resolve group membership, and temporarily exclude the user to confirm a Graph-dependent policy is the trigger.
- 4Verify outbound connectivity from the client / federation server (ADFS, Entra Connect) to graph.microsoft.com and login.microsoftonline.com — confirm no proxy, TLS inspection or firewall rule is blocking these endpoints.
- 5If the issue is reproducible across users and there is no Microsoft incident, open a support ticket with Microsoft including the correlation ID from the error page — only Microsoft can investigate Graph-side failures.