SQL Server Orphaned Users often appear after restoring or migrating a database to another server, where the user SID no longer matches the associated login. This mismatch blocks database access even when credentials are correct, causing login errors and operational delays. The issue usually occurs after backup restore, database migration, or when server logins are not transferred properly. Identifying orphaned users through system views and fixing them by remapping to existing logins or recreating missing ones can quickly restore access. For smoother handling during migration, tools like Aryson SQL Server Database Migration Tool can assist in maintaining proper user-login mapping and reducing access-related issues.