Are the archived items in primary mailbox or secondary mailbox? If they are from secondary mailbox you need to tick "Allow Scripts in shared Folders" and restart outlook.
For outlook 2003
click on Tools, Options, go to the Other tab, click on the Advanced Options and select "Allow script in shared folders".
For Outlook 2007
On the Tools menu, click Trust Center, Email Security, Under Script in Folders, enable 'Allow script in shared folders' and click ok and restart outlook.
What is the version of Enterprise Vault and EV client extensions installed on vista?