How did you deploy the forms?
What is the version of the EV Client?
Check the following:
With Enterprise Vault (EV) 2007, the forms are now included with the client extensions and can be deployed via the mailbox policy. Perform the following to deploy the forms:
1. Open the vault administration console
2. Expand Enterprise Vault | Site name | Policies | Exchange | Mailbox
3. Properties of the appropriate policies | Advanced tab
4. From the drop down menu, choose Outlook
5. Set the policy Deploy Forms Locally to Always
6. Synchronize all mailboxes