Solution by Event Log Doctor

This error is usually logged when a desktop action is unable to send a mailslot message to the EventSentry management console.

This can be either be due to the management console (eventsentry_gui.exe) not running or not being configured to show desktop alerts.

If you are not using desktop notifications, then you can simply disable or delete the "Desktop" action.

If you would like to use desktop notifications, open the management console and navigate to Tools -> Options -> General and make sure that one of the two tray area notification options are selected under "Show notification as". Select either the "Popup Window" or "Balloon" notification type.

Please also note that when you plan on sending desktop notifications to a remote management console, that you need to specify a valid hostname in the desktop action. A dot "." in the hostname field results in the EventSentry agent sending notifications to the local host, which might is not desirable in most cases.