As a test logon to the Active Administrator server using the service account credentials and try to open Active Directory Users and Computers. If you get an error like the one below it might be that there is an issue with your service account or DNS issues, or a major issue with your domain controllers.
If there are no issues with your domain controllers, or DNS records, then create a new service account and run AA Configuration Wizard to configure Active Administrator to run with this new service account.