You may recieve the below error in the Archive Manager event log.
Event Type: Error
Event Source: Message Retention Policy Service
Event Category: None
Event ID: 0
Time: 12:00:01 AM
Retention.Service: Cannot load policy set: Could not find a PolicySet named RetentionPolicySetIdentifier
If the Archive Manager Message Retention Policy Service is Started and the Retention Policy Editor has never been installed or launched you will receive this error when the Message Retention Policy Service scheduler kicks off at 12:00 a.m.
If the retention service is not used to delete items out of Archive Manager, disable the Archive Manager Message Retention Policy Service and this will stop the error from occurring.