The performance counter "Process(*)\% Processor Time" (instance "SWEEPSRV.SYS") which previously exceeded the configured threshold, is not available anymore and will not be monitored.
This message is logged when an instance of a performance counter that had previously triggered an alert is not available anymore. This event effectively clears a previous alert since the instance has gone away.
For example, a process might have been using more than 90% CPU time and EventSentry generated an alert. The above message is logged when this process exits before the alarm can be cleared.
This feature can be configured at "Packages -> System Health Packages -> Package Name -> Performance Monitoring -> "+" (add a performance counter) or "-" (remove a performance counter)".