“The ability to detect events, make sense of them and determine the appropriate control action”† is provided by Event Management. Event Management is therefore the basis for Operational Monitoring and Control.
Both statements are correct. A Known Error is raised when the root cause of an Incident has been diagnosed and a workaround (permanent or temporary) has been identified. There may also be occasions when there is sufficient reason (benefit) to create a Known Error even if the exact cause is not known. In ITIL the phrase for this situation is ‘as soon as it becomes useful’.
This is the ITIL definition of an Alert. Alerts are managed by the Event Management process.