AADSTS500571 – Guest User Account Disabled

Error: AADSTS500571 – The guest user account is disabled

This error typically happens when your named user account (used for delegated admin access) has been added to the customer tenant as a guest user — usually from SharePoint, OneDrive, or Teams sharing.

Cause: Microsoft blocks access via guest accounts if they’re disabled or conflict with delegated access roles. This affects named users much more than dedicated service accounts.

Resolution

Option 1 – Check and Remove Guest Account in Customer Tenant

1. Login to the customer’s Microsoft Entra ID portal
2. Navigate to Users → Guest users
3. Search for the delegated admin account (e.g., your named user)
4. If found, delete the guest user record from the customer tenant

Option 2 – Use a Service Account Instead of a Named User

To avoid this issue permanently, create a dedicated service account in your partner tenant for delegated admin access.

See setup guidance: 3 – Configure Microsoft 365 Partner Admin Account