Agents show as "Inactive" on the Agent Statistics tab of the ChangeAuditor Client. The agent logs show issues connecting to the coordinator.
This can occur if the Coordinator doesn't connect to SQL properly after a reboot of the SQL server. The Coordinator log may not show signs of any issue. You only see the agent log messages and an inactive status in the Client.
Restarting the Quest ChangeAuditor Coordinator or Agent Services will usually correct this issue. You can restart the service via "Start" | "Run..." | "services.msc", or by Right-Clicking the Coordinator Tray Icon and selecting "Disable Coordinator" then "Enable Coordinator".
Monitor "Agent Statistics" to make sure agents don't start going inactive again.