Harry,
The A2 queue is used for manual archiving. So the first question needs to be why are these items stuck in the queue and not being archived. If you purge the queue then the user that has tried to manually archive a mail will have their mail stuck in an archive pending state.
Are there any messages in the enterprise vault event log? You should be able to purge by signing on as VSA and purging which will move them to the admin queue and then they need to be purged from there. Sometimes items are indeed purged as when you try to look inside the queue there are no messages but it does report that they are stll in there.
Paul