Confirm there are no firewalls blocking communication between the workstations and the AA server over port 15601. Ensure the AA server is listening on port 15601 and the workstations can connect to the server on that port.
Ensure that the AA server and all of the workstations have a PTR record in DNS. If PTR records are missing, create the records and remove and reinstall the Workstation Logon Audit agents.
Confirm the Workstation Logon Agents have been deployed properly by reviewing the following KB articles: