Manually enable Offline Vault on the client by setting the following registry value:
1. Go to Start | Run and type "Regedit" to open the Windows Registry.
2. Navigate to HKEY_CURRENT_USER\Software\KVS\Enterprise Vault\Client.
3. Right-click on Client and choose New | DWORD Value.
4. Type the name OVEnabled and set it to a value of 1.
5. Restart Outlook for the change to take affect.