I'm using MS Outlook 2007 on Vista with a 3rd party mailing service on a POP3 Account without Exchange Server. I've been using it for abt a year without any issues. Today morning suddenly when I tried to open my Sent Folders it gave me an error message `The messaging interface has returned an unknown error. If the problem persists, restart Outlook.' I've done that and even restarted my system, but still cant access my Sent folder. Can anyone help me on this.