ArcGIS Data Store returns an error message, "...returned an error. Failed to log in. Invalid username or password specified" when validating through the ArcGIS Server admin endpoint.

Workaround

In most cases, this issue is fixed by unregistering and re-registering the relational data store.

In some cases, the relational data store must be restored back from a backup. Once registered back, the Portal for ArcGIS URL repopulates.

Schritte zur Reproduzierung