"A security package specific error occurred. Exception from HRESULT: 0x80070721 (1), please check support pages"
If you see this error in the Connector logs or in the dashboard, it means that you've registered a Read-Only Domain Controller as an AD server in the dashboard under Sites & Active Directory.
Currently, Read-Only Domain Controllers are not supported and will cause issues if left registered in the Dashboard. We recommend removing the Read-Only Domain Controller from the Dashboard and removing any components installed on it.
As long as there is at least one Domain Controller with the Connector installed, the domain should sync without issue even if a Read-Only Domain Controller is present in the Domain.