Symptoms
The K2 server could not find the worklist item 00000_000. This item may have been actioned by another user.
The full error from the K2 server is 'The worklist item 00000_000 is no longer available or you do not have rights to open it.'.
Diagnoses
When a node loses connectivity with SQL, it thinks it has lost connectivity to the farm, and so it reprocesses SmartAction emails.
Resolution
The customer was provided a coldfix for SQL connectivity loss in a K2 farm scenario.