I hit the same error.

When creating a Unity Catalog metastore from the web UI of the Azure Databricks Account Console, the following error appeared during Access Connector validation, despite having all the Azure configuration correctly set up (managed identity, IAM role, scope, hierarchical namespace, network, account permissions).

The error was a defect/overly strict validation in the web UI, not an actual configuration problem. The solution was to run the same process through the Databricks CLI, which completed the operation without errors.