Conceptually, events in Oracle Enterprise Manager are equivalent to messages in OMU. In OMU, a message is information generated for the operation whenever an event occurs.
In OMU, the term acknowledge has a different meaning than for most applications. Acknowledging a message in OMU means that an event has been resolved and the message is closed.
Note:
Do not acknowledge messages in OMU that have originated in Enterprise Manager. This will cause errors to occur whenever the corresponding event in Enterprise Manager is updated (changed severity, clears, etc.) and the connector tries to update the message in OMU.