Anyone know what the cause of this error is? Failed to remove the expired entries from the document history table.

The document history table is used by IS to implement exactly once functionality. Document ID’s are either kept only in memory or, if client-side queueing in enabled, they are stored in disk in addition to memory. Documents are deleted from history after the number of minutes in the “Duration” field. Setting the duration field to 0 disables exactly once processing. The default value is 10 minutes.

The error you are seeing occurs when the server can’t delete documents from the document history table. I think this may be a “normal” error if there are no documents in the history to be deleted. I can reproduce that error by clicking on the “Remove Expired Document History Entries” link on the “Settings > Resources > Exactly Once Statistics” page when there are no documents in the history table.

Beginning in 6.1, exactly once processing can be configured at the individual trigger level by setting properties in Developer rather than only globally. This allows you to activate exactly once processing only where you need that functionality and it makes sense to take the performance hit of the additional disk i/o it requires.