I'd be inclined to think you may be getting the error due to a long running query/report on your DB. Therefore I'd have receommended either a). A larger retention time or b). Run the query/report out of the main business hours.

Julian, could you explain why decreasing the retention period would reduce the occurance because it has me a little confused, as Oracle and my own experience tell me to increase. But maybe I'm the one confused

Cheers,