I had a similar issue with Outlook 2010 and EV not being a visible tab on the Outlook ribbon. This was a new laptop and after confirming EV was installed and wasn't a disabled admin I checked the ev client log under \users\username\appdata\local\temp\ev_client_log*.txt.
My error was
23/08/2013 14:04:09.394[3244][H]: Log file created (level 1).
23/08/2013 14:04:09.395[3244][H]: Loaded UI Language Path: c:\program files (x86)\enterprise vault\evclient\languages\en
23/08/2013 14:04:09.396[3244][H]: Loaded Help Language Path: c:\program files (x86)\enterprise vault\evclient\languages\en
23/08/2013 14:04:09.397[3244][H]: Module path: C:\Program Files (x86)\Enterprise Vault\EVClient\valkyrie.dll
23/08/2013 14:04:09.397[3244][H]: No language resource module was loaded, the default English resources in Valkyrie.dll will be used
23/08/2013 14:04:09.398[3244][H]: RPC over HTTP is enabled (flags = 39)
23/08/2013 14:04:09.431[3244][H]: Unknown exception occurred23/08/2013 14:04:09.461[3244][H]: IDispatch::GetIDsOfNames("MessageClass") failed, error 80020006
23/08/2013 14:04:09.483[3244][H]: FUI: Not loading UI as action map is empty. Is the user enabled?
Since this was a new laptop I compared the EV logs on my old laptop and found that I had caused the problem myself because I had migrated my \users\username\sharepoint sites folder from the old laptop to the new. I deleted the objects in that folder and re-opened outlook and the tab appeared.
